Student Support Material Class XII Physics
Student Support Material Class XII Physics
Student Support Material Class XII Physics
PHYSICS
Class-XII
INDEX
SYLLABUS
Session 2020-21
PHYSICS
CLASS-XII
Marks
Unit–I Electrostatics
Chapter–1: Electric Charges and Fields
Chapter–2: Electrostatic Potential and Capacitance 16
DELETED TOPICS
(for Session 2020-21)
PHYSICS
CLASS XII
S.No Name of the Chapter Deleted Topics
01 Electric charges and uniformly charged thin spherical shell (field inside and
fields outside).
02 Current Electricity Carbon resistors, colour code for carbon resistors;
series and parallel combinations of resistors
03 Cyclotron
Moving Charges and
Magnetism
04 Magnetism and Matter magnetic field intensity due to a magnetic dipole
(bar magnet) along its axis and perpendicular to its
axis, torque on a magnetic dipole (bar magnet) in a
uniform magnetic field;
Para-, dia- and ferro - magnetic substances, with
examples. Electromagnets and factors affecting their
strengths, permanent magnets.
05 Alternating Current power factor, wattless current
06 Electromagnetic Waves Basic idea of displacement current
07 Ray Optics and Optical Reflection of light, spherical mirrors,(recapitulation)
Instruments mirror formula ,
UNIT-I ELECTROSTATISC
Assertion (A) & Reason(R)
For question numbers 1 to 20, two statements are given-one labelled Assertion (A)
and the other labelled Reason (R). Select the correct answer to these questions from
the codes (a), (b), (c) and (d) as given below.
a) Both A and R are true and R is the correct explanation of A
b) Both A and R are true but R is NOT the correct explanation of A
c) A is true but R is false
d) A is false and R is also false
1. Assertion (A): The electrostatics force increases with decrease the distance between the
charges.
Reason (R): The electrostatic force of attraction or repulsion between any two stationary
point charges is inversely proportional to the square of the distance between them.
Answer: A
2. Assertion(A): The Coulomb force between two points charges depend upon the dielectric
constant of the intervening medium.
Reason(R): Coulomb’s force varies inversely with the dielectric constant of medium.
Answer: A
3. Assertion(A): The charge given to a metallic sphere does not depend on whether it is
hollow or solid
Reason(R): The charge resides only at the surface of conductor.
Answer: A
4. Assertion (A): A comb run through one’s dry hair attracts small bits of paper.
Reason(R): Molecules in the paper gets polarized by the charged comb resulting in net
force of attraction
Answer: A
5. Assertion(A): A proton is placed in a uniform electric field, it tend to move along the
direction of electric field.
Reason(R): A proton is placed in a uniform electric field it experiences a force.
Answer: B
6. Assertion(A): Electric field at the surface of a charged conductor is always normal to the
surface at every point.
Reason(R): Electric field gives the magnitude & direction of electric force
⃗⃗⃗ ) experienced by any charge placed at any point.
(𝐹
Answer: B
Physics / XII (2020-21)
Answer: D
8. Assertion(A): Electric filed lines not form closed loops.
Reason(R): Electric filed lines are always normal to the surface of a conductor.
Answer: B
9. Assertion(A): No work is done in moving a test charge from one point to another over an
equipotential surface.
Reason(R): Electric field is always normal to the equipotential surface at every point
Answer: B
10. Assertion(A): No work is done in moving a point charge 𝑄 around a circular arc of radius ′𝑟′
at the Centre of which another point charge ′𝑞′ is located.
Reason(R): No work is done in moving a test charge from one point to another over an
equipotential surface.
Answer: A
11. Assertion(A): A metal plate is introduced between the plates of a charged parallel plate
capacitor, its capacitance increased.
Reason(R): A metal plate is introduced between the plates of a charged parallel plate
capacitor, the effective separation between the plates is decreased.
Answer: A
12. Assertion(A): In the presence of external electric field the net electric field within the
conductor becomes zero.
Reason(R): In the presence of external electric field the free charge carriers move and
charge distribution in the conductor adjusts itself.
Answer: A
13. Assertion (A): Sensitive instruments can protect from outside electrical influence by
enclosing them in a hollow conductor.
Reason(R): Potential inside the cavity is zero.
Answer: C
14. Assertion(A): Earthing provides a safety measure for electrical circuits and
appliances.
Reason(R): When we bring a charged body in contact with the earth, all the
excess charge on the body disappears by causing a momentary current to
pass to the ground through the connecting conductor.
Answer: A
Physics / XII (2020-21)
15. Assertion(A): The total amount of charge on a body equal to 4X10 -19 C is not
possible.
Reason(R): Experimentally it is established that all free charges are integral
multiples of a basic unit of charge denoted by e. Thus, charge q on a body is
always given by q = ne
Answer: A
16. Assertion(A): The net force on a dipole in a uniform electric dipole is zero.
Reason(R): Electric dipole moment is a vector directed from –q to +q.
Answer: B
is, as mentioned above, a very general result. A related result is that even if the conductor
is charged or charges are induced on a neutral conductor by an external field, all charges
reside only on the outer surface of a conductor with cavity.
The proofs of the results noted in Fig. are omitted here, but we note their important
implication. Whatever be the charge and field configuration outside, any cavity in a
conductor remains shielded from outside electric influence: the field inside the cavity is
always zero. This is known as electrostatic shielding. The effect can be made use of in
protecting sensitive instruments from outside electrical influence.
(1) A metallic shell having inner radius R1 and outer radii R2 has a point charge Q kept
inside cavity. Electric field in the region R1 < r < R2 where r is the distance from the
centre is given by
(a) depends on the value of r
(b) Zero
(c) Constant and nonzero everywhere
(d) None of the above
(5) Which of the following material can be used to make a Faraday cage (based on
electrostatic shielding)
(a) Plastic
(b) Glass
(c) Copper
(d) Wood
Answer: 1. b 2. d 3. b 4. a 5. c
Physics / XII (2020-21)
2. When a glass rod is rubbed with silk, the rod acquires one kind of charge and the silk
acquires the second kind of charge. This is true for any pair of objects that are rubbed to
be electrified. Now if the electrified glass rod is brought in contact with silk, with which it
was rubbed, they
no longer attract
each other. They
also do not attract
or repel other light
objects as they did
on being
electrified.
Thus, the charges
acquired after
rubbing are lost
when the charged bodies are brought in contact. What can you conclude from these
observations? It just tells us that unlike charges acquired by the objects neutralise or nullify
each other’s effect. Therefore, the charges were named as positive and negative by the
American scientist Benjamin Franklin. We know that when we add a positive number to a
negative number of the same magnitude, the sum is zero. This might have been the
philosophy in naming the charges as positive and negative. By convention, the charge on
glass rod or cat’s fur is called positive and that on plastic rod or silk is termed negative. If
an object possesses an electric charge, it is said to be electrified or charged. When it has
no charge it is said to be electrically neutral.
(1) When you charge a balloon by rubbing it on your hair this is an example of what
method of charging?
(a)Friction
(b)Conduction
(c)Grounding
(d)Induction
(2) Neutral atoms contain equal numbers of positive __ and negative __.
(a)Electrons and Protons
(b)Protons and Electrons
(c)Neutrons and Electrons
(d)Protons and Neutrons
(4) If a negatively charged rod touches a conductor, the conductor will be charged by
what method?
(a) Friction
(b)Conduction
(c)Induction
(d)Convection
Physics / XII (2020-21)
Answer: 1. a 2. b 3. b 4. b 5. C
3. For electrostatics, the concept of electric field is convenient, but not really necessary.
Electric field is an elegant way of characterizing the electrical environment of a system of
charges. Electric field at a point in the space around a system of charges tells you the force
a unit positive test charge would experience if placed at that point (without disturbing the
system). Electric field is a characteristic of the system of charges and is independent of the
test charge that you place at a point to determine the field. The term field in physics
generally refers to a quantity that is defined at every point in space and may vary from
point to point. Electric field is a vector field, since force is a vector quantity.
(1) Which of the following statement is correct? The electric field at a point is
(a) always continuous.
(b) continuous if there is a charge at that point.
(c) discontinuous only if there is a negative charge at that point.
(d) discontinuous if there is a charge at that point.
(4) The magnitude of electric field intensity E is such that, an electron placed in it
would experience an electrical force equal to its weight is given by
(a) mge
(b) mg/e
(c) e/mg
(d) e²g/m²
(5) At a particular point, Electric field depends upon
(a) Source charge Q only
(b) Test Charge q0 only.
(c)Both q and q0
(d)Neither Q nor q0
Answer: 1. b 2. b 3. c 4. b 5. a
Physics / XII (2020-21)
4. Dielectric with
polar molecules
also develops a
net dipole moment
in an external
field, but for a
different reason.
In the absence of
any external field,
the different
permanent dipoles
are oriented
randomly due to
thermal agitation;
so
the total dipole
moment is zero.
When
an external field is
applied, the
individual dipole
moments tend to alignwith the field. When summed overall the molecules, there is then a
net dipole moment in the direction of the external field, i.e., the dielectric is polarised. The
extent of polarisation depends on the relative strength of two factors: the dipole potential
energy in the external field tending to align the dipoles mutually opposite with the field and
thermal energy tending to disrupt the alignment. There may be, in addition, the ‘induced
dipole moment’ effect as for non-polar molecules, but generally the alignment effect is
more important for polar molecules. Thus in either case, whether polar or non-polar, a
dielectric develops a net dipole moment in the presence of an external field. The dipole
moment per unit volume is called polarization.
Answer: 1. b 2. a 3. b 4. b 5. C
5. Figure (a) shows an uncharged metallic sphere on an insulating metal stand. If we Bring
a negatively charged rod close to the metallic sphere, as shown in Fig. (b). As the rod is
brought close to the sphere, the free electrons in the sphere move away due to repulsion
and start piling up at the farther
end. The near end becomes
positively charged due to deficit
of electrons.
This process of charge
distribution stops when the net
force on the free electrons
inside the metal is zero. Now if
we Connect the sphere to the
ground by a conducting wire.
The electrons will flow to the
ground while the positive
charges at the near end will
remain held there due to the
attractive force of the negative
charges on the rod, as shown in Fig. (c). Disconnect the sphere from the ground. The
positive charge continues to be held at the near end Fig.(d). if we remove the electrified
rod. The positive charge will spread uniformly over the sphere as shown in Fig. (e). In this
experiment, the metal sphere gets charged by the process of induction and the rod does
not lose any of its charge.
(1) What do you call the process of charging a conductor by bringing it near another
Charged object?
(a) Induction
(b) Polarisation
(c) neutralization
(d) conduction
Physics / XII (2020-21)
(2) The negatively charged balloon is brought near the two cans. What happens?
(4) Due to electrostatic induction in aluminum rod due to charged plastic rod, the total
charge on the aluminum rod is
(a)Zero
(b)Positive
(c) Negative
(d) Dual
(5) If we bring charged plastic rod near-neutral aluminum rod, then rods will
(a)Repel each other
(b)Attract each other
(c)Remain their position
(d)Exchange charges
Answer: 1. a 2. b 3. b 4. a 5. b
Physics / XII (2020-21)
A) If both Statement I and Statement II are true and the statement II is the correct
explanation of the statement I.
B) If both Statement I and Statement II are true but statement II is not the correct
explanation of the statement I.
C) If Statement I is true but Statement II is false.
D) If the Statement I and Statement II both are false.
E) If Statement I is false but Statement II is true.
Answer: A
Q2:
A) If both Statement I and Statement II are true and the statement II is the correct
explanation of the statement I.
B) If both Statement I and Statement II are true but statement II is not the correct
explanation of the statement I.
C) If Statement I is true but Statement II is false.
D) If the Statement I and Statement II both are false.
E) If Statement I is false but Statement II is true.
Answer: A
Q3:
A) If both Statement I and Statement II are true and the statement II is the correct
explanation of the statement I.
B) If both Statement I and Statement II are true but statement II is not the correct
explanation of the statement I.
Physics / XII (2020-21)
A) If both Statement I and Statement II are true and the statement II is the correct
explanation of the statement I.
B) If both Statement I and Statement II are true but statement II is not the correct
explanation of the statement I.
C) If Statement I is true but Statement II is false.
D) If the Statement I and Statement II both are false.
E) If Statement I is false but Statement II is true.
Answer: A
Q5:
A) If both Statement I and Statement II are true and the statement II is the correct
explanation of the statement I.
B) If both Statement I and Statement II are true but statement II is not the correct
explanation of the statement I.
C) If Statement I is true but Statement II is false.
D) If the Statement I and Statement II both are false.
E) If Statement I is false but Statement II is true.
Answer: D
Physics / XII (2020-21)
Q6:
A) If both Statement I and Statement II are true and the statement II is the correct
explanation of the statement I.
B) If both Statement I and Statement II are true but statement II is not the correct
explanation of the statement I.
C) If Statement I is true but Statement II is false.
D) If the Statement I and Statement II both are false.
E) If Statement I is false but Statement II is true.
Answer: A
Q7:
A) If both Statement I and Statement II are true and the statement II is the correct
explanation of the statement I.
B) If both Statement I and Statement II are true but statement II is not the correct
explanation of the statement I.
C) If Statement I is true but Statement II is false.
D) If the Statement I and Statement II both are false.
E) If Statement I is false but Statement II is true.
Answer: C
Q8:
A) If both Statement I and Statement II are true and the statement II is the correct
explanation of the statement I.
B) If both Statement I and Statement II are true but statement II is not the correct
explanation of the statement I.
C) If Statement I is true but Statement II is false.
D) If the Statement I and Statement II both are false.
E) If Statement I is false but Statement II is true.
Answer: A
Physics / XII (2020-21)
Q9:
A) If both Statement I and Statement II are true and the statement II is the correct
explanation of the statement I.
B) If both Statement I and Statement II are true but statement II is not the correct
explanation of the statement I.
C) If Statement I is true but Statement II is false.
D) If the Statement I and Statement II both are false.
E) If Statement I is false but Statement II is true.
Answer: D
Q10:
A) If both Statement I and Statement II are true and the statement II is the correct
explanation of the statement I.
B) If both Statement I and Statement II are true but statement II is not the correct
explanation of the statement I.
C) If Statement I is true but Statement II is false.
D) If the Statement I and Statement II both are false.
E) If Statement I is false but Statement II is true.
Answer: B
Q11:
Physics / XII (2020-21)
A) If both Statement I and Statement II are true and the statement II is the correct
explanation of the statement I.
B) If both Statement I and Statement II are true but statement II is not the correct
explanation of the statement I.
C) If Statement I is true but Statement II is false.
D) If the Statement I and Statement II both are false.
E) If Statement I is false but Statement II is true.
Answer: A
Q12:
A) If both Statement I and Statement II are true and the statement II is the correct
explanation of the statement I.
B) If both Statement I and Statement II are true but statement II is not the correct
explanation of the statement I.
C) If Statement I is true but Statement II is false.
D) If the Statement I and Statement II both are false.
E) If Statement I is false but Statement II is true.
Answer: D
Q13:
A) If both Statement I and Statement II are true and the statement II is the correct
explanation of the statement I.
B) If both Statement I and Statement II are true but statement II is not the correct
explanation of the statement I.
C) If Statement I is true but Statement II is false.
D) If the Statement I and Statement II both are false.
E) If Statement I is false but Statement II is true.
Answer: D
Physics / XII (2020-21)
Q14:
Statement 1: The possibility of an electric bulb fusing is higher at the time of switching ON
and OFF
Statement 2: Inductive effects produce a surge at the time of switch ON and OFF
A) If both Statement 1 and Statement 2 are true and the statement 2 is the correct
explanation of the statement 1.
B) If both Statement 1 and Statement 2 are true but statement 2 is not the correct
explanation of the statement 1.
C) If Statement 1 is true but Statement 2 is false.
D) If the Statement 1 and Statement 2 both are false.
E) If Statement 1 is false but Statement 2 is true.
Answer: A
Q15:
Statement 1: The 200 W bulbs glow with more brightness than 100 W bulbs.
Statement 2: A 100 W bulb has more resistance than a 200 W bulb.
A) If both Statement 1 and Statement 2 are true and the statement 2 is the correct
explanation of the statement 1.
B) If both Statement 1 and Statement 2 are true but statement 2 is not the correct
explanation of the statement 1.
C) If Statement 1 is true but Statement 2 is false.
D) If the Statement 1 and Statement 2 both are false.
E) If Statement 1 is false but Statement 2 is true.
Answer: A
Q16:
Statement 1: Fuse wire must have high resistance and low melting point.
Statement 2: Fuse is used for small current flow only.
A) If both Statement 1 and Statement 2 are true and the statement 2 is the correct
explanation of the statement 1.
B) If both Statement 1 and Statement 2 are true but statement 2 is not the correct
explanation of the statement 1.
C) If Statement 1 is true but Statement 2 is false.
D) If the Statement 1 and Statement 2 both are false.
E) If Statement 1 is false but Statement 2 is true.
Answer: C
Q17:
Statement 1: Two electric bulbs of 50 and 100 W are given. When connected in series 50
W bulb glows more but when connected parallel 100 W bulb glows more.
Statement 2: In series combination, power is directly proportional to the resistance of the
circuit. But in parallel combination, power is inversely proportional to the resistance of the
circuit.
Physics / XII (2020-21)
A) If both Statement 1 and Statement 2 are true and the statement 2 is the correct
explanation of the statement 1.
B) If both Statement 1 and Statement 2 are true but statement 2 is not the correct
explanation of the statement 1.
C) If Statement 1 is true but Statement 2 is false.
D) If the Statement 1 and Statement 2 both are false.
E) If Statement 1 is false but Statement 2 is true.
Answer: A
Q18:
Statement 1: Two bulbs of same wattage, one having a carbon filament and the other
having a metallic filament are connected in series. Metallic bulbs will glow more brightly
than a carbon filament bulb.
Statement 2: Carbon is a semiconductor.
A) If both Statement 1 and Statement 2 are true and the statement 2 is the correct
explanation of the statement 1.
B) If both Statement 1 and Statement 2 are true but statement 2 is not the correct
explanation of the statement 1.
C) If Statement 1 is true but Statement 2 is false.
D) If the Statement 1 and Statement 2 both are false.
E) If Statement 1 is false but Statement 2 is true.
Answer: D
Q19:
Statement 1: An electric bulb is first connected to a dc source and then to an ac source
having the same brightness in both cases.
Statement 2: The peak value of voltage for an A.C. source is √2 times the root mean
square voltage.
A) If both Statement 1 and Statement 2 are true and the statement 2 is the correct
explanation of the statement 1.
B) If both Statement 1 and Statement 2 are true but statement 2 is not the correct
explanation of the statement 1.
C) If Statement 1 is true but Statement 2 is false.
D) If the Statement 1 and Statement 2 both are false.
E) If Statement 1 is false but Statement 2 is true.
Answer: E
Q20:
Statement 1: Current is passed through a metallic wire, heating it red. When cold water is
poured on half of its portion, then the rest of the half portion becomes hotter.
Statement 2: Resistances decrease due to a decrease in temperature and so current
through wire increases.
Physics / XII (2020-21)
A) If both Statement 1 and Statement 2 are true and the statement 2 is the correct
explanation of the statement 1.
B) If both Statement 1 and Statement 2 are true but statement 2 is not the correct
explanation of the statement 1.
C) If Statement 1 is true but Statement 2 is false.
D) If the Statement 1 and Statement 2 both are false.
E) If Statement 1 is false but Statement 2 is true.
Answer: A
Q21:
Statement 1: Through the same current flows through the line wires and the filament
of the bulb but the heat produced in the filament is much higher than that in line wires.
Statement 2: The filament of bulbs is made of a material of high resistance and a
high melting point.
A) If both Statement 1 and Statement 2 are true and the statement 2 is the correct
explanation of the statement 1.
B) If both Statement 1 and Statement 2 are true but statement 2 is not the correct
explanation of the statement 1.
C) If Statement 1 is true but Statement 2 is false.
D) If the Statement 1 and Statement 2 both are false.
E) If Statement 1 is false but Statement 2 is true.
Answer: A
Q22:
Statement 1: In practical application, the power rating of resistance is not important.
Statement 2: Property of resistance remain the same even at high temperature.
A) If both Statement 1 and Statement 2 are true and the statement 2 is the correct
explanation of the statement 1.
B) If both Statement 1 and Statement 2 are true but statement 2 is not the correct
explanation of the statement 1.
C) If Statement 1 is true but Statement 2 is false.
D) If the Statement 1 and Statement 2 both are false.
E) If Statement 1 is false but Statement 2 is true.
Answer: D
Q23:
Statement 1: Leclanche cell is used, when a constant supply of electric current is not
required.
Statement 2: The e.m.f. of a Leclanche cell falls, if it is used continuously.
Physics / XII (2020-21)
A) If both Statement 1 and Statement 2 are true and the statement 2 is the correct
explanation of the statement 1.
B) If both Statement 1 and Statement 2 are true but statement 2 is not the correct
explanation of the statement 1.
C) If Statement 1 is true but Statement 2 is false.
D) If the Statement 1 and Statement 2 both are false.
E) If Statement 1 is false but Statement 2 is true.
Answer: A
Q24:
Statement 1: In the given circuit if lamp B or C fuses then the light emitted by lamp A
decreases.
Statement 2: Voltage on A decreases.
A) If both Statement 1 and Statement 2 are true and the statement 2 is the correct
explanation of the statement 1.
B) If both Statement 1 and Statement 2 are true but statement 2 is not the correct
explanation of the statement 1.
C) If Statement 1 is true but Statement 2 is false.
D) If the Statement 1 and Statement 2 both are false.
E) If Statement 1 is false but Statement 2 is true.
Answer: A
Q25:
Statement 1: If three identical bulbs are connected in series as shown in figure then on
closing the switches. Bulb C short-circuited and hence illumination of bulbs A and B
decreases.
Statement 2: Voltage on A and B decreases
A) If both Statement 1 and Statement 2 are true and the statement 2 is the correct
explanation of the statement 1.
B) If both Statement 1 and Statement 2 are true but statement 2 is not the correct
explanation of the statement 1.
C) If Statement 1 is true but Statement 2 is false.
D) If the Statement 1 and Statement 2 both are false.
E) If Statement 1 is false but Statement 2 is true.
Answer: D
Physics / XII (2020-21)
Q26:
Statement 1: Heat is generated continuously is an electric heater but its temperature
becomes constant after some time.
Statement 2: At the stage when heat produced in the heater is equal to the heat dissipated
to its surrounding the temperature of the heater becomes constant.
A) If both Statement 1 and Statement 2 are true and the statement 2 is the correct
explanation of the statement 1.
B) If both Statement 1 and Statement 2 are true but statement 2 is not the correct
explanation of the statement 1.
C) If Statement 1 is true but Statement 2 is false.
D) If the Statement 1 and Statement 2 both are false.
E) If Statement 1 is false but Statement 2 is true.
Answer: A
Q27:
Statement 1: Electric appliances with a metallic body; e.g. heaters, presses, etc, have
three-pin connections, whereas an electric bulb has a two pin connection.
Statement 2: Three-pin connections reduce the heating of connecting cables.
A) If both Statement 1 and Statement 2 are true and the statement 2 is the correct
explanation of the statement 1.
B) If both Statement 1 and Statement 2 are true but statement 2 is not the correct
explanation of the statement 1.
C) If Statement 1 is true but Statement 2 is false.
D) If the Statement 1 and Statement 2 both are false.
E) If Statement 1 is false but Statement 2 is true.
Answer: C
Q28:
Statement 1: A domestic electrical appliance, working on a three-pin will continue working
even if the top pin is removed.
Statement 2: The third pin is used only as a safety device.
A) If both Statement 1 and Statement 2 are true and the statement 2 is the correct
explanation of the statement 1.
B) If both Statement 1 and Statement 2 are true but statement 2 is not the correct
explanation of the statement 1.
C) If Statement 1 is true but Statement 2 is false.
D) If the Statement 1 and Statement 2 both are false.
E) If Statement 1 is false but Statement 2 is true.
Answer: A
Physics / XII (2020-21)
Q29:
Statement 1: The presence of water molecules makes separation of ions easier in an
electrolyte.
Statement 2: The presence of water molecules in electrolyte decreases the resistance of
electrolyte.
A) If both Statement 1 and Statement 2 are true and the statement 2 is the correct
explanation of the statement 1.
B) If both Statement 1 and Statement 2 are true but statement 2 is not the correct
explanation of the statement 1.
C) If Statement 1 is true but Statement 2 is false.
D) If the Statement 1 and Statement 2 both are false.
E) If Statement 1 is false but Statement 2 is true.
Answer: B
A: Efficiency of kettle A is
1. 63.34%
2. 83.34%
3. 93.34%
4. 73.34%
B: Efficiency of kettle B is
1. 82.5%
2. 72.5%
3. 92.5%
4. 62.5%
C: Ratio of efficiency consumed charges for one time boiling of tea in kettle A to that in
kettle B
1. 3:5
2. 2:3
3. 3:4
4. 1:1
D: If the resistance of the coil in kettle A and B is Ra and Rb then we can say
1. Ra>Rb
2. Ra=Rb
3. Ra<Rb
4. Data insufficient
E: If both the kettles are joined with the same source in series one after another then
boiling starts in kettle A and kettle B after
1. 4 times of their original time
2. Equal to their original time
3. 2 times of their original time
4. Data insufficient
Answers:
A. 2
B. 4
C. 3
D. 2
E. 1
Q2: Consider an evacuated cylindrical chamber of height h having rigid conducting plates
at the ends and an insulating curved surface as shown in the figure. A number of spherical
balls made of a light weight and soft material and coated with a conducting material are
placed on the bottom plate. The balls have a radius r«h. Now a high voltage source (HV) is
connected across the conducting plates such that the bottom plate is at + V, and the top
plate at - Vo. Due to their conducting surface, the balls will get charged, will become
equipotential with the plate and are repelled by it. The balls will eventually collide with the
top plate, where the coefficient of restitution can be taken to be zero due to the soft nature
of the material of the balls. The electric field in the chamber can be considered to be that of
Physics / XII (2020-21)
a parallel plate capacitor, Assume that there are no collisions between the balls and the
interaction between them is negligible. (Ignore gravity)
Q3:
Answers:
A. 3
B. 1
C. 1
Q4
R is nearly 10 ohm ) is
1. Zero in both cases
2. Non-zero but equal in both cases
3. More in circuit A
4. More in circuit B
Answers:
A. 2
B. 2
C. 4
Q6
Answers:
A. 3
B. 1
C. 1
Q7.
Physics / XII (2020-21)
A: Two fuse wires of same potential material are having length ratio 1:2 and ratio
4:1 Then respective ratio of their current rating will be
1. 8:1
2. 2:1
3. 1:8
4. 4:1
B: The maximum power rating of a 20.0 ohm fuse wire is 2.0 kW,then this fuse
wire can be connected safely to a DC source (negligible internal resistance) of
1. 300 volt
2. 190 volt
3. 250 volt
4. 220 volt
C: Efficiency of a battery when delivering maximum power is
1. 100 %
2. 50 %
3. 90 %
4. 40 %
Answers:
A. 1
B. 2
C. 4
Physics / XII (2020-21)
Q8
1.
2.
3.
4.
𝑅2
B: The ratio of is
𝑅3
1.
2.
3.
4.
C: The current that passes through the resistance R2 nearest to the V0 is
1.
2.
3.
Physics / XII (2020-21)
4.
Answers:
A. 4
B. 3
C. 4
Q10 An ammeter and a voltmeter are connected in series to a battery with an emf
of 10V. When a certain resistance is connected in parallel with the voltmeter, the
reading of the voltmeter decreases three times, whereas the reading of the
ammeter increases two times.
B: If the resistance of the ammeter is 2 ohm, then the resistance of the voltmeter
is:-
1. 1 ohm
2. 2 ohm
3. 3 ohm
4. 4 ohm
Answers:
A. 2
B. 3
C. 1
Physics / XII (2020-21)
1. Assertion(A):
The centripetal force on the test charge qo is qo vB, where v is the velocity of a
particle and B is the magnetic field.
Reason (R):
When a charged particle is fired at right angles to the magnetic field, the radius of its
circular path is directly proportional to the kinetic energy of the particle.
2. Assertion (A):
Magnetic field due to an infinite straight conductor varies inversely as the distance
from it.
Reason (R):
The magnetic field due to a straight conductor is in the form of concentric circles.
3. Assertion (A):
A rectangular current loop is in an arbitrary orientation in an external uniform
magnetic field. No work is required to rotate the loop about an axis perpendicular to
the plane of loop
Reason (R):
All positions represent the same level of energy.
4. Assertion (A):
The magnitude of magnetic field in a region is equal to the number of magnetic field
lines per unit area where area should be normal to the field.
Reason (R):
Magnetic field is tangential to a magnetic field line.
5. Assertion (A):
If a proton and an α-particle enter a uniform magnetic field perpendicularly with the
same speed, the time period of revolution of α-particle is double than that of proton.
Physics / XII (2020-21)
Reason (R):
In a magnetic field, the period of revolution of a charged particle is directly
proportional to the mass of the particle and inversely proportional to the charge of
the particle.
6. Assertion (A):
A charged particle is moving in a circular path under the action of a uniform
magnetic field. During the motion, kinetic energy of the charged particle is constant.
Reason (R):
During the motion, magnetic force acting on the particle is perpendicular to
instantaneous velocity.
7. Assertion (A):
When radius of a circular loop carrying current is doubled, its magnetic moment
becomes four times.
Reason (R):
Magnetic moment depends on the area of the loop.
8. Assertion (A):
The magnetic field at the ends of a very long current carrying solenoid is half of that
at the centre.
Reason (R):
If the solenoid is sufficiently long, the field within it is uniform.
9. Assertion (A):
If an electron and proton enter a magnetic field with equal momentum, then the
paths of both of them will be equally curved.
Reason (R):
The magnitude of charge on an electron is same as that on a proton.
Reason (R):
The magnitudes of magnetic fields are equal and the directions of magnetic fields
due to both the semicircles are opposite.
16. Assertion (A):
The voltage sensitivity may not necessarily increase on increasing the current
sensitivity.
Reason (R):
Current sensitivity increases on increasing the number of turns of the coil.
Reason (R):
Magnetic force on a charge particle is given by F = (IL x B).
ANSWER KEY:
1. c 11. a
2. b 12. a
3. a 13. d
4. b 14. b
5. a 15. a
6. a 16. b
7. a 17. c
8. b 18. d
9. a 19. a
10. a 20. c
A point charge q (moving with a velocity v and located at r at a given time t) in the
presence of both the electric field E and magnetic field B. The force on an electric
charge q due to both of them can be written as
F = q [ E + v x B ] = Fel + Fmag
It is called the ‘Lorentz force’.
Physics / XII (2020-21)
1. If the charge q is moving under a field, the force acting on the charge depends on
the magnitude of field as well as the velocity of the charge particle, what kind of field
is the charge moving in?
(a) Electric field
(b) Magnetic field
(c) Both electric and magnetic field perpendicular to each other
(d) None of these
2. The magnetic force acting on the charge ‘q’ placed in a magnetic field will vanish
if
(a) if v is small
(b) If v is perpendicular to B
(c) If v is parallel to B
(d) None of these
4. The vectors which are perpendicular to each other in the relation for magnetic
force acting on a charge particle are
(a) F and v
(b) F and B
(c) v and B
(d) All of these
2. An electron, proton, He+ and Li++ are projected with the same velocity
perpendicular to a uniform magnetic field. Which one will experience maximum
magnetic force?
(a) Electron
(b) Proton
(c) He+
(d) Li++
3. The work done by the magnetic field on the charge particle moving perpendicular
to a uniform magnetic field is
(a) Zero
(b) q (v x B). S
(c) Maximum
(d) qBS/v
4. The distance moved by a charged particle along the magnetic field in one
rotation, when v has a component parallel to B is
2v cos
(a)
qBm
2mv cos
(b)
qB
qBm
(c)
2v cos
Physics / XII (2020-21)
Bq
(d)
2m
During a solar flare, a large number of electrons and protons are ejected from the
sun. Some of them get trapped in the earth’s magnetic field and move in helical
paths along the field lines. The field lines come closer to each other near the
magnetic poles, hence the density of charges increases near the poles. The
particles collide with atoms and molecules of the atmosphere. Excited oxygen atoms
emit green light and excited nitrogen atoms emit pink light. This phenomenon is
called ‘Aurora Borealis’.
1. When will the path of the particle be helix, when it is moving in external magnetic
field?
(a) When v has a component parallel to B
(b) When v has a component perpendicular to B
(c) When v is parallel to B
(d) None of these
2. When the charged particle travelling in a helical path enters a region where the
magnetic field is non-uniform, the pitch of helix of the charge particle will be
(a) Same as in uniform magnetic field
(b) Increases as the charge moves inside the magnetic field
(c) Decreases as the charge moves inside the magnetic field
(d) First increases then decreases as the charge moves inside the magnetic field
3. The colour of Aurora Borealis is due to
(a) Excited ozone, chromium atoms
(b) Excited Oxygen and Nitrogen atoms
(c) Due to presence of water vapours in the atmosphere
(d) Excited electrons and protons in the atmosphere
A charge q moving with a velocity v in presence of both electric and magnetic fields
experience a force F = q [ E + v x B ]. If electric and magnetic fields are
perpendicular to each other and also perpendicular to the velocity of the particle, the
electric and magnetic forces are in opposite directions. If we adjust the value of
electric and magnetic field such that magnitude of the two forces are equal. The
total force on the charge is zero and the charge will move in the fields undeflected.
1.What will be the value of velocity of the charge particle, when it moves undeflected
in a region where the electric field is perpendicular to the magnetic field and the
charge particle enters at right angles to the fields.
(a) v = E/B
(b) v = B/E
(c) v = EB
(d) v = EB/q
2. Proton, neutron, alpha particle and electron enter a region of uniform magnetic
field with same velocities. The magnetic field is perpendicular to the velocity. Which
particle will experience maximum force?
(a) proton
(b) electron
(c) alpha particle
(d) neutron
3. A charge particle moving with a constant velocity passing through a space without
any change in the velocity. Which can be true about the region?
(a) E = 0, B = 0
(b) E ≠ 0, B ≠ 0
(c) E = 0, B ≠ 0
(d) All of these
4. Proton, electron and deuteron enter a region of uniform magnetic field with same
electric potential-difference at right angles to the field. Which one has a more curved
trajectory?
Physics / XII (2020-21)
(a) electron
(b) proton
(c) deuteron
(d) all will have same radius of circular path
A charged particle of mass m and charge q moves with a constant velocity along the
positive X direction v = ai. It enters a region of magnetic field which is directed
towards positive Z direction from x = a which is given by B = bk
1.The initial acceleration of the particle is
𝑞𝑎𝑏
(a) a = - i
𝑚
𝑞𝑎𝑚
(b) a = - j
𝑏
𝑞𝑎
(c) a = - j
𝑚𝑏
(d) none of these
3. Which of the following is true about the motion of the particle in uniform magnetic
field, where the charged particle enters at right angles to the field?
(a) Force will always be perpendicular to the velocity.
(b) Kinetic energy of the particle remains constant.
(c) Velocity vector and magnetic field vector remains perpendicular to each other
during the motion.
(d) All of these.
5. If the rectangular coil used in the moving coil galvanometer is made circular, then
what will be the effect on the maximum torque acting on the coil in magnetic field for
the same area of the coil?
(a) remains the same
(b) becomes less in circular coil
(c) becomes greater in circular coil
(d) depends on the orientation of the coil
Physics / XII (2020-21)
6.What is the torque and force in the two cases as shown in the fig.?
In the Bohr model of the Hydrogen atom, the electron revolves around a positively
charged nucleus such as a planet revolves around the sun. The force which binds
the electron-proton system is the electrostatic force. There will be a magnetic
moment associated with this circulating current given by M = I A.
1.What will be the magnetic moment of the electron in the first orbit of H-atom?
𝑒𝑣𝑟
(a) 2
𝑒𝑣
(b)2𝑟
𝑒𝑣
(c) 2𝑟𝑚
𝑒𝑣𝑟
(d) 2𝑚
2. The relation between magnetic moment and angular momentum for an electron
revolving in the first orbit of H-atom is
𝑒
(a) M = 2𝑚 L
𝑒
(b) L = 2𝑚 M
𝑒𝐵
(c) M = 2𝑚 L
𝑒𝐵
(d) L = 2𝑚 M
Physics / XII (2020-21)
3. The angle between magnetic moment vector and angular momentum vector is
(a) 0°
(b)45°
(c)90°
(d)180°
The magnetic field lines of the earth resemble that of a hypothetical magnetic dipole
located at the centre of the earth. The axis of the dipole does not coincide with the
axis of rotation of the earth but is presently tilted by approximately 11.3° with respect
to the later. If the magnetic needle is perfectly balanced about a horizontal axis so
that it can swing in a plane of the magnetic meridian, the needle would make an
angle with the horizontal. This is known as the angle of dip (also known as
inclination).
1.What is the angle of dip at the equator?
(a) 0°
(b) 45°
(c) 60°
(d) 90°
2. At the poles, the dip needle will
(a) stay horizontal
(b) stay vertical
(c) stays at 45° angle with the horizontal
(d) does not remain steady in any fixed position
Physics / XII (2020-21)
3.The angle of dip where the vertical component of the earth’s magnetic field is
equal to the horizontal component of the earth’s magnetic field will be
(a)0°
(b)45°
(c)60°
(d)90°
4. Which of the following independent quantities is not used to specify the earth’s
magnetic field?
(a) Magnetic declination (θ)
(b) Angle of dip (δ)
(c) Horizontal component of earth’s magnetic field (BH)
(d) Vertical component of earth’s magnetic field (BV)
Two current-carrying conductors placed near each other will exert magnetic forces
on each other. Ampere studied the nature of this magnetic force and its dependence
on the product of magnitude of currents in both the conductors, on the shape and
size of conductors as well as the distances between the conductors. Using
Fleming’s left hand rule, it is observed that currents flowing in the same direction
attract each other and currents flowing in the opposite directions repel each other.
Thus, force per unit length acting on a conductor of infinite length is given by
µ0 𝐼1 𝐼2
F=
2𝜋 𝑑
1.A vertical wire carries a current in upward direction. An electron beam sent
horizontally towards the wire will be deflected
(a)towards right
(b)towards left
(c)upwards
(d)downwards
2. A current carrying, straight wire is kept along axis of a circular loop carrying a
current. The straight wire
(a)will exert an inward force on the circular loop.
(b)will exert an outward force on the circular loop.
(c)will not exert any force on the circular loop.
(d)will exert a force on the circular loop parallel to itself.
Physics / XII (2020-21)
3. A proton beam is going from north to south and electron beam is going from
south to north. Neglecting the earth’s magnetic field, the electron beam will be
deflected
(a)towards the proton beam
(b)away from the proton beam
(c)upwards
(d)downwards
4. Consider the situation shown in fig. The straight wire is fixed but the loop can
move under magnetic force. The loop will
(a)remain stationary
(b)move towards the wire
(c)move away from the wire
(d) rotate about the wire.
1.The magnetic field inside a toroid of radius R is B. If the current through it is doubled and
its radius is also doubled keeping the number of turns per unit length the same, magnetic
field produced by it will be
(a) B/2
(b) B/4
(c)B
(d)2B
2. What is the magnetic field in the empty space enclosed by the toroid of radius R?
µ 2𝐼
(a)4𝜋0 𝑅
(b) Infinity
(c) Zero
µ 𝜋𝐼
(d) 4𝜋0 𝑅
UNIT-IV
ELECTROMAGNETIC INDUCTION AND ALTERNATING
CURRENT
ASSERTION (A) & REASONING (R) QUESTIONS
Of the following statements, mark the correct Answers as-
A - if both Assertion and Reason -- are true and Reason -- is correct explanation of the Assertion.
B - if both Assertion and Reason -- are true but Reason -- is not correct explanation of Assertion.
C - if Assertion is true but Reason -- is false.
D - if both Assertion and Reason -- are false.
E - if Assertion is false but Reason -- is true
1. Assertion-- The mutual induction of two coils is doubled, if the self-inductance of the
primary or secondary coil is doubled
Reason -- Mutual induction is proportional to self-inductance of primary and secondary
coils
Answer - C
2. Assertion- Making and breaking of current in a coil produce no momentary current in the
neighboring coil of another circuit
Reason -- Momentary current in the neighboring coil of another circuit is an eddy current
Answer - D
4. Assertion- An electric motor will have maximum efficiency when back emf becomes
equal to half of applied emf
Reason -- Efficiency of electric motor depends only on magnitude of back emf
Answer – C
5. Assertion- Armature current in DC motor is maximum when the motor has just started
Reason -- Armature current is given by I=E-e/R where e is back emf, R is resistance of
armature
Answer – B
6. Assertion- Eddy current is produced in any metallic conductor when magnetic flux is
changed around it
Reason -- Electric potential determine the flow of charge
Answer - B
9. Assertion- Only a change in magnetic flux through a coil maintain a current in the coil if
the current is continues
Reason -- The presence of large magnetic flux through a coil maintain a current in the coil
if the current is continues
Answer - C
13. Assertion- an aircraft flies along the meridian, the potential at the ends of its wings will
be the same.
Reason -- Whenever there is change in magnetic flux emf induce
Answer – E
14. Assertion- A spark occur between the poles of a switch when the switch is opened
Reason -- Current flowing in the conductor produce magnetic field
Answer – B
16. An induced emf is generated when magnet is withdrawn from the solenoid
Reason -- The relative motion between the magnet and solenoid induced emf
Answer - A
27. Eddy current is produced in any metallic conductor when magnetic flux is changed
around it
Reason -- electric potential determine the flow of charge
Answer – B
28. In LCR circuit resonance can take place
Reason -- resonance can take place if inductance and capacitive reactance are equal and
opposite
Answer - A
29. When capacitive reactance is smaller than the inductive reactance in LCR circuit, emf
leads the current
Reason -- The phase angle is angle between alternating emf and alternating current of the
circuit
Answer – B
Let a current i flows through the inductor from A to B. Whenever electric current changes
through it, a back emf is generated. If the resistance of inductor is assumed to be zero
(ideal inductor) then induced emf in it is given by
e=VB-VA = - L di / dt
Thus, potential drops across an inductor as we movein the direction of current. But
potential also drops across a pure resistor when we move in the direction of the current.
The main difference between a resistor and an inductor is that while a resistor opposes the
current through it, an inductor opposes the change in current through it.
Now answer the following questions.
(1) How does inductor behave when
(a) a steady current flow through it?
(b) a steadily increasing, current flows through it?
(c) a steadily decreasing current flows through it?
(d) Name the phenomenon in which change in current in a coil induces EMF in coil itself?
(b) A closed loop moves normal to the constant electric field between the plates of a large
capacitor. Is a current induced in the loop
(i) when it is wholly inside the region between the capacitor plates
(ii) when it is partially outside the plates of the capacitor? The electric field is normal to the
plane of the loop.
Physics / XII (2020-21)
(c) A rectangular loop and a circular loop are moving out of a uniform magnetic field region
(Figure) to a field-free region with a constant velocity v. In which loop do you expect the
induced emſ to be constant during the passage out of the field region? The field is normal
to the loops.
(d) Predict the polarity of the capacitor in the situation described by the figure
Solution:
(a) No. However strong the magnet may be current can be induced only by changing the
magnetic flux through the loop.
(b) No current is induced in either case. Current can not be induced by changing the
electric flux.
(c) The induced emf is expected to be constant only in the case of the rectangular loop. In
the case of circular loop, the rate of change of area of the loop during its passage out of
the field region is not constant, hence induced emf will vary accordingly,
(d) The polarity of plate 'A' will be positive with respect to plate 'B' in the capacitor.
Question 3:
Given figure shows a metal rod PQ resting on the smooth rails AB and positioned between
the poles of a permanent magnet. The rails, the rod, and the magnetic field are in three
mutual perpendicular directions. A galvanometer G connects the rails through a switch K.
Length of the rod = 15 cm, B = 0.50 T, resistance of the closed loop containing the rod =
9.0 mΩ. Assume the field to be uniform.
(a) Suppose K is open and the rod is moved with a speed of 12 cm s -1 in the direction
shown. Give the polarity and magnitude of the induced emf.
Physics / XII (2020-21)
(b) Is there an excess charge built up at the ends of the rods when K is open? What if K is
closed?
(c) With K open and the rod moving uniformly, there is no net force on the electrons in the
rod PQ even though they do experience magnetic force due to the motion of the rod.
Explain.
(d) What is the retarding force on the rod when K is closed?
(e) How much power is required (by an external agent) to keep the rod moving at the same
speed (=12 cm/ sec) when K is closed? How much power is required when K is open?
(f) How much power is dissipated as heat in the closed circuit? What is the source of this
power?
(g) What is the induced emf in the moving rod if the magnetic field is parallel to the rails
instead of being perpendicular?
Answers:
(a) EMF = vBL = 0.12 0.50 x 0.15 = 9.0 mV;
P positive end and Q negative end.
(b) Yes. When K is closed, the excess charge is maintained by the continuous flow of
current.
(c) Magnetic force is cancelled by the electric force set-up due to the excess charge of
opposite signs at the ends of the rod.
(d) Retarding force = IBL
9 mV / 9 mΩ x 0.5 T x 0.15 m
= 75 x 10-3 N
e) Power expended by an external agent against the above retarding
force to keep the rod moving uniformly at 12 cm s'
= 75 x 10-3 x 12 x 10-2 = 9.0 x 10-3 W
When K is open, no power is expended.
Question 3:
A small town with a demand of 800 kW of electric power at 220 V is situated 15 km away
from an electric plant generating power at 440 V. The resistance of the two wire line
carrying power is 0.5Ω per km. The town gets power from the line through a 4000-220 V
step-down transformer at a sub-station in the town.
(a) Estimate the line power loss in the form of heat.
(b) How much power must the plant supply, assuming there is negligible power loss due to
leakage?
(c) Characterise the step up transformer at the plant.
Answers:
Line resistance = 30 X 0.5 = 15Ω
rms current in the line . 800 x 1000 W / 4000 V = 200 A
Physics / XII (2020-21)
4. What will be the acceleration of the falling bar magnet which passes through the ring
such that the ring is held horizontally and the bar magnet is dropped along the axis
of the ring?
(a) It depends on the diameter of the ring and the length of the magnet
(b) It is equal due to gravity
(c) It is less than due to gravity
(d) It is more than due to gravity
Answer: (c) It is less than due to gravity
Physics / XII (2020-21)
UNIT-V
ELECTROMAGNETIC WAVES
ASSERTION (A) AND REASONING (R) QUESTIONS
A. Both assertion and reason are True, and reason is the correct explaination .
B. Both assertion and reason are True, but reason is not the correct explaination .
C. Assertion is True , but reason is False .
D. Both assertion and reason are False .
Assertion: The EM waves of shorter wavelength can travel longer distances on earth’s
surface than those of longer wavelengths.
Reason: Shorter the wavelength, the larger is the Velocity of propagation.
Answer: C
Assertion : Like Light radiation, thermal radiations are also e.m. radiations .
Reason: Thermal radiations require no medium for propagation .
Answer: B
Microwave are used in aircraft navigation. A radar guns out short bursts of microwave and
it reflect back from oncoming aircraft and are detected by receiver in gun. The frequency of
reflected wave used to compute speed of aircraft
ANSWER KEY
1)a 3)c
2)b 4)a
Q3) X- Rays
X-rays are a form of electromagnetic radiation, similar to visible light. Unlike light, however,
x-rays have higher energy and can pass through most objects, including the body. Medical
x-rays are used to generate images of tissues and structures inside the body.
Physics / XII (2020-21)
Q2) which of the following set of instrument /equipment can detect X- rays
a) Photocells ,photographic film
b) Thermopiles ,bolometer
c) Photographic film ,Geiger tube
d) Geiger tube ,human eye
Q4) what is the use of rays lying beyond X ray region in electromagnetic spectrum
a) used to kill microbes
b) used to detect heat loss in insulated systems
c) used in standard broadcast radio and television
d) used In oncology, to kill cancerous cells.
ANSWER KEY
Q1 c Q2 c
Q3 b Q4 d
Q3) which of the following is the best method for production of infrared waves
a) bombardment of metal by high energy electrons
b) radioactive decay of nucleus
c) magnetron valve
d) vibration of atoms and molecules
(ANSWER KEY)
Q1 b Q2 a
Q3 d Q4 b
Q4. What physical quantity is the same for X rays of wavelength 10-10m, red light of
wavelength 6800 Ao and radiowaves of wavelength 500m?
I) Speed in vacuum (c)
II) frequency (f)
III) Scattering
IV) Energy (e)
ANSWER KEY
1. II) PRODUCTION AND DETECTION OF WAYS
2. IV) EXPLOSIVES
3. III) GAMMA RAYS AND RADIO WAVES
4. I) SPEED IN VACUUM
Physics / XII (2020-21)
UNIT-VI
OPTICS
Instructions:
Two statements are given-one labelled Assertion (A) and the other labelled Reason
(R). Select the correct answer to these questions from the codes (a), (b), (c) and (d)
as given below.
a) Both A and R are true and R is the correct explanation of A
b) Both A and R are true but R is NOT the correct explanation of A
c) A is true but R is false
d) A is false and R is also false
3) Assertion : A double convex lens (μm = 1.5) has focal length 10 cm. When the lens is
immersed in water (μl = 4/3) its focal length becomes 40 cm.
Reason : 1/f = [(μl−μm)/μm](1/R1−1/R2)
Correct Answer: A
Solution : Focal length of lens immersed in water is four times the focal length of
lens in air. It means
fw = 4fa = 4×10 = 40 cm
4) Assertion : The colour of the green flower seen through red glass appears to be dark.
Reason : Red glass transmits only red light.
Correct Answer: A
Solution : The red glass absorbs the radiations emitted by green flowers; so flower
appears black.
5) Assertion : The mirrors used in search lights are parabolic and not concave spherical.
Reason : In a concave spherical mirror the image formed is always virtual.
Correct Answer: C
Physics / XII (2020-21)
Solution : In search lights, we need an intense parallel beam of light. If a source is placed
at the focus of a concave spherical mirror, only paraxial rays are rendered parallel. Due to
large aperture of mirror, marginal rays give a divergent beam. But in case of parabolic
mirror, when source is at the focus, beam of light produced over the entire cross-section of
the mirror is a parallel beam.
6) Assertion : The size of the mirror affect the nature of the image.
Reason : Small mirrors always forms a virtual image.
Correct Answer: D
Solution : The size of the mirror does not affect the nature of the image except that a
bigger mirror forms a brighter image.
7) Assertion : Within a glass slab, a double convex air bubble is formed. This air bubble
behaves like a converging lens.
Reason : Refractive index of air is more than the refractive index of glass.
Correct Answer: D
Solution : The air bubble would behave as a diverging lens, because refractive index of air
is less than refractive index of glass. However, the geometrical shape of the air bubble
shall resemble a double convex lens.
8) Assertion : The focal length of lens does not change when red light is replaced by blue
light.
Reason : The focal length of lens does not depends on colour of light used.
Correct Answer: D
Solution : Focal length of the lens depends upon it's refractive index as 1/f ∝ (μ−1). Since
μb > μr so fb < fr . Therefore, the focal length of a lens decreases when red light is replaced
by blue light.
10) Assertion : A beam of white light gives a spectrum on passing through a hollow prism.
Reason : Speed of light outside the prism is different from the speed of light inside the
prism.
Correct Answer: D
Physics / XII (2020-21)
Solution : Dispersion of light cannot occur on passing through air contained in a hollow
prism. Dispersion take place because the refractive index of medium for different colour is
different. Therefore when white light travels from air to air, refractive index remains same
and no dispersion occurs.
11) Assertion : If objective and eye lenses of a microscope are interchanged then it can
work as telescope. Reason : The objective of telescope has small focal length.
Correct Answer: D
Solution : We cannot interchange the objective and eye lens of a microscope to make a
telescope. The reason is that the focal length of lenses in microscope are very small, of the
order of mm or a few cm and the difference (fo & fe) is very small, while the telescope
objective have a very large focal length as compared to eye lens of microscope.
12) Assertion : Although the surfaces of a goggle lens are curved, it does not have any
power.
Reason : In case of goggles, both the curved surfaces have equal radii of curvature.
Correct Answer: A
Solution : The focal length of a lens is given by 1/f=(μ−1)(1/R1−1/R2) For, goggle, R1 = R2
1/ f= (μ−1)(1/R1−1/R2) = 0. Therefore, P = 1/f = 0.
13) Assertion : If the angles of the base of the prism are equal, then in the position of
minimum deviation, the refracted ray will pass parallel to the base of prism.
Reason : In the case of minimum deviation, the angle of incidence is equal to the angle of
emergence.
Correct Answer: A
Solution : In case of minimum deviation of a prism ∠i=∠e. so, ∠r1=∠r2
14) Assertion : An empty test tube dipped into water in a beaker appears silver, when
viewed from a suitable direction.
Reason : Due to refraction of light, the substance in water appears silvery.
Correct Answer: C
Solution : The ray of light incident on the water air interface suffers total internal
reflections, in that case the angle of incidence is greater than the critical angle. Therefore,
if the tube is viewed from suitable direction (so that the angle of incidence is greater than
the critical angle), the rays of light incident on the tube undergoes total internal reflection.
As a result, the test tube appears as highly polished i.e. silvery.
is called marginal rays. In case of lens having large aperture, the behaviour of the paraxial
and marginal rays are markedly different from each other. The two types of rays come to
focus at different points on the principal axis of the lens, thus the spherical aberration
occur. However in case of a lens with small aperture, the two types of rays come to focus
quite close to each other.
16) Assertion : The frequencies of incident, reflected and refracted beam of monochromatic
light incident from one medium to another are same
Reason : The incident, reflected and refracted rays are coplanar.
Correct Answer: B
Solution : If both assertion and reason are true but reason is not the correct explanation
of the assertion.
17) Assertion : By roughening the surface of a glass sheet its transparency can be
reduced.
Reason : Glass sheet with rough surface absorbs more light.
Correct Answer: C
Solution : When glass surface is made rough then the light falling on it is scattered in
different direction due to which its transparency decreases.
(ii) In the above diagram, calculate the speed of light in the liquid of unknown refractive
index.
a) 1.2 × 108 m/𝑠
b) 1.4 × 108 m/𝑠
c) 1.6 × 108 m/𝑠
d) 1.8 × 108 m/𝑠
(iii) What is refractive index of a medium(in terms of real and apparent depth).
a) Real depth/ App depth
b) App/ Real depth
c) App Real depth
d) Real + App depth
(iv) What is the relation between refractive index and critical angle for a medium.
a) n = 1/sin ic
b) n = sin ic
c) 1 = n/ sin ic
d) None of the above
Answer:
i) (b)
ii) (d)
iii) (a)
iv) (a)
(i) What is the principal behind Advance sunrise and delayed sunset.
(a) Reflection.
(b) Refraction.
c) Dispersion
d) Total internal reflection.
(ii) For how much time the sun is visible apparently after sunset.
(a) Approx. 5 minutes
b) Approx. 10 minutes
Physics / XII (2020-21)
c) Approx. 2 minutes
d) None of the above
Answers
i) (b)
ii) (c)
iii) (b)
iv) (b)
3) Optical fibres: Now-a-days optical fibres are extensively used for transmitting audio and
video signals through long distances. Optical fibres too make use of the phenomenon of
total internal reflection. Optical fibres are fabricated with high quality composite
glass/quartz fibres. Each fibre consists of a core and cladding. The refractive index of the
material of the core is higher than that of the cladding. When a signal in the form of light is
directed at one end of the fibre at a suitable angle, it undergoes repeated total internal
reflections along the length of the fibre and
finally comes out at the other end. Since light undergoes total internal reflection at each
stage, there is no appreciable loss in the intensity of the light signal. Optical fibres are
fabricated such that light reflected at one side of inner surface strikes the other at an angle
larger than the critical angle. Even if the fibre is bent, light can easily travel along its length.
Thus, an optical fibre can be used to act as an optical pipe.
Answers
i) (b)
ii) (c)
iii) (c)
iv) (a)
PART - B
Wave Optics (Assertion and Reasoning Based Questions)
1) Assertion : When a light wave travels from a rarer to a denser medium, it loses speed.
The reduction in speed imply a reduction in energy carried by the light wave.
Reason : The energy of a wave is proportional to velocity of wave.
Correct Answer: D
Solution : When a light wave travel from a rarer to a denser medium it loses speed, but
energy carried by the wave does not depend on its speed. Instead, it depends on the
amplitude of wave.
2) Assertion : No interference pattern is detected when two coherent sources are infinitely
close to each other.
Reason : The fringe width is inversely proportional to the distance between the two slits.
Correct Answer: A
Solution : When d is negligibly small, fringe width β which is proportional to 1/d may
become too large. Even a single fringe may occupy the whole screen. Hence the pattern
cannot be detected.
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3) Assertion : For best contrast between maxima and minima in the interference pattern of
Young’s double slit experiment, the intensity of light emerging out of the two slits should be
equal.
4) Assertion: In Young’s experiment, the fringe width for dark fringes is different from that
for white fringes.
Reason : In Young’s double slit experiment the fringes are performed with a source of
white light, then only black and bright fringes are observed.
Correct Answer: D
Solution : In Young’s experiments fringe width for dark and white fringes are same while in
Young’s double slit experiment when a white light as a source is used, the central fringe is
white around which few coloured fringes are observed on either side.
5) Assertion : When a tiny circular obstacle is placed in the path of light from some
distance, a bright spot is seen at the centre of shadow of the obstacle.
Reason : Destructive interference occurs at the centre of the shadow.
Correct Answer: C
Solution : As the waves diffracted from the edges of circular obstacle, placed in the path
of light interfere constructively at the centre of the shadow resulting in the formation of a
bright spot.
6) Assertion : Interference pattern is made by using blue light instead of red light, the
fringes becomes narrower.
Reason : In Young?s double slit experiment, fringe width is given by relation β = λD/d.
Correct Answer: A
Solution : β = λD/d.
7) Assertion: Diffraction is common in sound but not common in light waves.
Reason : Wavelength of light is more than the wavelength of sound.
Answer (c)
Solution: If assertion is true but reason is false
10) Assertion : If complete YDSE (Young’s Double Slit Experiment) is dipped in the liquid
from the air, then fringe width decreases.
Reason : Wavelength of light decreases, when we move from air to liquid.
Answer: (a)
11) Assertion: No sustained interference pattern is obtained when two electric bulbs of the
same power are taken.
Reason: Phase difference between waves coming out of electric bulbs is not constant.
Answer: (a)
12) Assertion: The maximum intensity in YDSE (Young’s Double Slit Experiment) is four
times the intensity due to each slit when they are identical.
Reason: The phase difference between the interfering waves is 2nπ at the position of
maxima where n = 0, 1, 2, ......
Answer: (a)
ii) Which parameter remains unchanged while a ray of light propagates from one medium
to another?
a) velocity
b) Wave length
c) frequency
d) None of the above
iii) According to the above given fig., identify the correct expression for Snell’s law.
a) n1 sin i = n2 sin r
b) n2 sin i = n1 sin r
c) n21 = sin r/ sin i
d) None of the above
Answers:
i) (a)
ii) (c)
iii) (a)
iv) (c)
i) What is the path difference between the two light waves coming from coherent sources,
which produces 3rd maxima.
a)
b) 2
c) 3
d0
(i) In the phenomena of Diffraction of light when the violet light is used in the experiment is
used instead of red light then,
(a) Fringe width increases
(b) No change in fridge width
(c) Fringe width decreases
(d) Colour pattern is formed
(ii) Diffraction aspect is easier to notice in case of the sound waves then in case of the light
waves because sound waves
(a) Have longer wavelength
(b) Shorter wavelength
(c) Longitudinal wave
(d) Transverse waves
(iii) Diffraction effects show that light does not travel in straight lines. Under what condition
the concepts of ray optics are valid. ( D = distance of screen from the slit).
(a) D < Zf
(b) D = Zf
(c) D > Zf
(d) D << Zf
(iv) when 2nd secondary maxima is obtained in case of single slit diffraction pattern, the
angular position is given by
(a)
(b) /2
(c) 3/2
(d) 5/2
Answers:
(i) (c)
(ii) (a)
(iii) (d)
(iv) (d)
Physics / XII (2020-21)
UNIT-VII
DUAL NATURE OF RADIATION AND MATTER
Directions: In each of the following questions, a statement of Assertion (A) is given followed
by a corresponding statement of Reason (R) just below it. Of the statements, mark the
correct answer as:
(A)If both assertion and reason are true and reason is the correct explanation of assertion
(B)If both assertion and reason are true but reason is not the correct explanation of
assertion
(C)If assertion is true and reason is false
(D)If both assertion and reason are false
Answers
Q1. (a) Q2. (a) Q3. (c) Q4. (c) Q5. (a)
Q6. (a) Q7. (d) Q8. (b) Q9. (c) Q10. (d)
Q11. (d) Q12. (a) Q13. (b)
1. The photoelectric emission is possible only if the incident light is in the form of packets of
energy, each having a definite value, more than the work function of the metal. This shows
that light is not of wave nature but of particle nature. It is due to this reason that
photoelectric emission was accounted by quantum theory of light.
Q1. Packet of energy are called
(a)electron
(b)quanta
(c)frequency
(d)neutron
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Q4. Which of the following waves can produce photo electric effect
(a). UV radiation
(b). Infrared radiation
(c). Radio waves
(d) .Microwaves
Answer
Q1.(b) Q2.(c) Q3.(c) Q4.(a) Q5.(d)
Q2. According to de-Broglie a moving material particle sometimes acts as a wave and
sometimes as a particle or a wave is associated with moving material particle which
controls the particle in every respect. The wave associated with moving material particle is
called matter wave or de-Broglie wave whose wavelength called de-Broglie wavelength, is
given by λ = h/mv
1.The dual nature of light is exhibited by
(a) diffraction and photo electric effect
(b) photoelectric effect
(c) refraction and interference
(d)diffraction and reflection.
2. If the momentum of a particle is doubled , then its de-Broglie wavelength will
(a)remain unchanged (b)become four times
(c) become two times (d)become half
Physics / XII (2020-21)
3. If an electron and proton are propagating in the form of waves having the same
λ , it implies that they have the same
(a)energy (b)momentum
(c)velocity (d)angular momentum
4. Velocity of a body of mass m, having de-Broglie wavelength λ , is given by relation
(a) v = λ h/m (b) v = λm/h
(c) v = λ/hm (d) v = h/ λm
5. Moving with the same velocity , which of the following has the longest de Broglie
wavelength?
(a)ᵦ -particle (b) α -particle
(c) proton (d) neutron.
Answer
Q1.(a) Q2.(d) Q3.(b) Q4.(d) Q5.(a)
Physics / XII (2020-21)
UNIT-VIII
ATOM AND NUCLEUS
Instructions:
A) If both assertion and reason are true and the reason is the correct explanation of
the assertion.
B) If both assertion and reason are true but reason is not the correct explanation of
the assertion.
C) If assertion is true but reason is false.
D) If the assertion and reason both are false.
E) If assertion is false but reason is true.
1.
Assertion: It is not possible to use 35Cl as the fuel for fusion energy.
Reason: The binding energy of 35Cl is too small.
Correct Answer: C
Solution : In fusion, lighter nuclei are used so, fusion is not possible with 35Cl. Also
binding energy of 35Cl is not too small.
2.
Assertion : 90Sr from the radioactive fall out from a nuclear bomb ends up in the
bones of human beings through the milk consumed by them. It causes impairment of
the production of red blood cells.
Reason : The energetics b-particles emitted in the decay of 90Sr damage the bone
marrow.
Correct Answer: A
Solution : 90Sr38 decays to 90Y39 by the emission of β− rays. Sr gets absorbed in bones
along with calcium. Reason is also true.
3.
Assertion : Neutrons penetrate matter more readily as compared to protons.
Reason : Neutrons are slightly more massive than protons.
Correct Answer: B
Solution : Neutron is about 0.1 more massive than proton. But the unique thing about
the neutron is that while it is heavy, it has no charge (it is neutral). Thi s lack of
charge gives it the ability to penetrate matter without interacting as quickly as the
beta particles or alpha particles.
Physics / XII (2020-21)
4.
Assertion : Neutrons penetrate matter more readily as compared to protons.
Reason : Neutrons are slightly more massive than protons.
Correct Answer: B
Solution : Neutron is about 0.1 more massive than proton. But the unique thing about
the neutron is that while it is heavy, it has no charge (it is neutral). This lack of
charge gives it the ability to penetrate matter without interacting as quickly as the
beta particles or alpha particles.
5.
Assertion : Radioactive nuclei emit β−1 particles.
Reason : Electrons exist inside the nucleus.
Correct Answer: C
Solution : Nuclear stability depends upon the ratio of neutron to proton. If the n/p ratio
is more than the critical value, then a neutron gets converted into a proton forming
a β− particle in the process. So electrons do not exist in the nucleus but they result in
some nuclear transformation.
6.
Assertion : ZXA undergoes 2α decays 2β− decays and 2Ƴ decays and the daughter
product is Z−2YA−8.
Reason : In a-decay the mass number decreases by 4 and atomic number
decreases by 2. In b- decay the mass number remains unchanged, but atomic
number increases by 1 only.
Correct Answer: A
Solution : ZX
A → 2(2He4) + 2(−1e0) + 2γ + z−2XA−8
7.
Assertion : Density of all the nuclei is same.
Reason : Radius of nucleus is directly proportional to the cube root of mass number.
Correct Answer: A
Solution : Experimentally it is found that the average radius of a nucleus is given by R
= R0A1/3 where R0 = 1.1×10−15m = 1.1 fm and A = mass number.
Physics / XII (2020-21)
8.
Assertion : Isobars are the element having same mass number but different atomic
number.
Reason : Neutrons and protons are present inside nucleus.
Correct Answer: B
9.
Assertion : The force of repulsion between atomic nucleus and a-particle varies with
distance according to inverse square law.
Reason : Rutherford did a-particle scattering experiment.
Correct Answer: B
10.
Assertion : The positively charged nucleus of an atom has a radius of almost 10−15m.
Reason : In a-particle scattering experiment, the distance of closest approach for a-
particles is ≃ 10−15m.
Correct Answer: A
11.
Assertion : According to classical theory, the proposed path of an electron in
Rutherford atom model will be parabolic.
Reason : According to electromagnetic theory an accelerated particle continuously
emits radiation.
Correct Answer: E
continuously and the orbital radius will go on decreasing and form spiral and finally
the electron will fall on the nucleus.
12.
Assertion : Electrons in the atom are held due to coulomb forces.
Reason : The atom is stable only because the centripetal force due to Coulomb?s
law is balanced by the centrifugal force.
Correct Answer: C
Solution : According to postulates of Bohr?s atom model, the electron revolve round
the nucleus in fixed orbit of definite radii. As long as the electron is in a certain orbits
it does not radiate any energy.
13.
Assertion : The electron in the hydrogen atom passes from energy level n=4 to the
n=1 level. The maximum and minimum number of photon that can be emitted are six
and one respectively.
Reason : The photons are emitted when electron make a transition from the higher
energy state to the lower energy state.
Correct Answer: B
Solution : Maximum number of photon is given by all the transitions possible =4C2 =
6. Minimum number of transition = 1, that is directly jump from 4 to 1.
14.
Assertion : Hydrogen atom consists of only one electron but its emission spectrum
has many lines.
Reason : Only Lyman series is found in the absorption spectrum of hydrogen atom
whereas in the emission spectrum, all the series are found.
Correct Answer: B
Solution : When the atom gets appropriate energy from outside, then this electron
rises to some higher energy level. Now it can return either directly to the lower
energy level or come to the lowest energy level after passing through other lower
energy lends, hence all possible transitions take place in the source and many lines
are seen in the spectrum.
Physics / XII (2020-21)
15.
Assertion : It is essential that all the lines available in the emission spectrum will
also be available in the absorption spectrum.
Reason : The spectrum of hydrogen atom is only absorption spectrum.
Correct Answer: D
Solution : Emission transitions can take place between any higher energy level and
any energy level below it while absorption transitions start from the lowest energy
level only and may end at any higher energy level. Hence number of absorptions
transitions between two given energy levels is always less than the number of
emission transitions between same two levels.
16.
Assertion : For the scattering of a-particles at a large angles, only the nucleus of the
atom is responsible.
Reason : Nucleus is very heavy in comparison to α particle.
Correct Answer: A
17.
Assertion : All the radioactive elements are ultimately converted in lead.
Reason : All the elements above lead are unstable.
Correct Answer: C
Solution : All those elements which are heavier than lead are radioactive. This is
because in the nuclei of heavy atoms, besides the nuclear attractive forces,
repulsive forces between the protons are also effective and these forces reduce the
stability of the nucleus. Hence, the nuclei of heavier elements are being converted
into lighter and lighter elements by emission of radioactive radiation. When they are
converted into lead, the emission is stopped because the nucleus of lead is stable
(or lead is most stable elements in radioactive series).
Physics / XII (2020-21)
18.
Assertion : Amongst alpha, beta and gamma rays, a-particle has maximum
penetrating power.
Reason : The alpha particle is heavier than beta and gamma rays.
Correct Answer: D
19.
Assertion : The ionising power of β-particle is less compared to a-particles but their
penetrating power is more.
Reason : The mass of β-particle is less than the mass of a-particle.
Correct Answer: B
Solution : β particles, being emitted with very high speed compared to α particles,
pass very little time near the atoms of the medium. So the probability of the atoms
being ionised is comparatively less. But due to this reason, their loss of energy is
very slow and they can penetrate the medium through a sufficient depth.
20.
Assertion : The mass of b-particles when they are emitted is higher than the mass of
electrons obtained by other means.
Reason : β-particle and electron, both are similar particles.
Correct Answer: B
Solution : β-particles are emitted with very high velocity (up to 0.99 c). So,
according to Einstein?s theory of relatively, the mass of a β -particle is much higher
compared to is` its rest mass (m0). The velocity of electrons obtained by other
means is very small compared to c (Velocity of light). So its mass remains nearly m0.
But b-particle and electron both are similar particles.
Correct Answer : C
22.
Assertion : Fragments produced in the fission of U235 are radioactive.
Reason : The fragments have abnormally high proton to neutron ratio.
Correct Answer: C
Solution : Fragments produced in the fission of U235 are radioactive. When uranium
undergoes fission, barium and krypton are not the only products. Over 100 different
isotopes of more than 20 different elements have been detected among fission
products. All of these atoms are, however, in the middle of the periodic table, with
atomic numbers ranging from 34 to 58. Because the neutron-proton ratio needed for
stability in this range is much smaller than that of the original uranium nucleus, the
residual nuclei called fission fragments, always have too many neutrons for stability.
A few free neutrons are liberated during fission and the fission fragments undergo a
series of beta decays (each of which increases Z by one and decreases N by one)
until a stable nucleus is reached. During decay of the fission fragments, an average
of 15 MeV of additional energy is liberated.
23.
Assertion : The mass of a nucleus can be either less than or more than the sum of
the masses of nucleons present in it.
Reason : The whole mass of the atom is considered in the nucleus.
Correct Answer: E
Solution : The whole mass of the atom is concentrated at nucleus and M(nucleus) <
(Sum of the masses of nucleus) because, when nucleous combines, some energy is
wasted.
24.
Assertion : Only those nuclei which are heavier than lead are radioactive.
Reason : Nuclei of elements heavier than lead are unstable.
Correct Answer : D
Solution : Some lighter nuclei are also radioactive.
25.
Assertion : In one half-life of a radioactive substance more number of nuclei are decayed
than in one average life.
Reason : Average life = Half -life/Ln (2)
Correct Answer : D)
Physics / XII (2020-21)
Solution : Average life is more Hence more nuclei decay in one average life .
26.
Assertion : Nucleus of the atom does not contain electrons, yet it emits β−particles in the form of
electrons.
Reason : In the nucleus, protons and neutrons exchange mesons frequently.
Correct Answer D
Solution : Nucleus of the atom does not contain electrons, yet it emits β− particles in the form of
electrons. The nucleus contains only protons and neutrons but In the nucleus, protons and
neutrons do not exchange mesons frequently.
Q3. If number of protons in an atom is equal to (number of electrons + 2). Then the atom is
said to be
a) Single ionized positive ion
b) Single ionized positive atom
c) Double ionized positive ion
d) Double ionized positive atom
Answer : Q1 – a; Q2 – b; Q3 – c; Q4 – b
Q1. The formula which gives the wavelength of emitted photon when electron jumps from
higher nergy state to lower was given by
a) Balmer
b) Paschen
c) Lymen
d) Rydberg
Physics / XII (2020-21)
Answer : Q1 – d; Q2 – b; Q3 – c; Q4 – b
Q2. From R = R0 A1/3 how can we conclude that density of almost all the nucleus is same
a) Volume being proportional to square of R density becomes independent of mass
number A
b) Volume being proportional to cube of R density becomes independent of mass
number A
c) Volume being proportional to R density becomes independent of mass number A
d) Density has no relation with R
Q3. What is the kinetic energy of α-particles bombarded towards the gold nucleus in
Geiger and Marsden classic experiment?
a) 8.8x10-13 Joule
b) 8.8x10-15 Joule
c) 8.8x10-13 Joule
d) x 10-13 Joule
e) 8.5x10-13 Joule
Answer : Q1 – b; Q2 – b; Q3 – a; Q4 – a
particle could get very close to the positive charge without penetrating it, and such a close
encounter would result in a large deflection. This agreement supported the hypothesis of
the nuclear atom. This is why Rutherford is credited with the discovery of the nucleus.
In Rutherford’s nuclear model of the atom, the entire positive charge and most
of the mass of the atom are concentrated in the nucleus with the electrons some distance
away. The electrons would be moving in orbits about the nucleus just as the planets do
around the sun. Rutherford’s experiments suggested the size of the nucleus to be about
10–15 m to 10–14 m. From kinetic theory, the size of an atom was known to be 10 –10 m,
about 10,000 to 100,000 times larger than the size of the nucleus. Thus, the electrons
would seem to be at a distance from the nucleus of about 10,000 to 100,000 times the size
of the nucleus itself. Thus, most of an atom is empty space. With the atom being largely
empty space, it is easy to see why most α -particles go right through a thin metal foil.
However, when α-particle happens to come near a nucleus, the intense electric field there
scatters it through a large angle. The atomic electrons, being so light, do not appreciably
affect the α-particles. The scattering data shown in Fig. can be analysed by employing
Rutherford’s nuclear model of the atom. As the gold foil is very thin, it can be assumed that
α-particles will suffer not more than one scattering during their passage through it.
Therefore, computation of the trajectory of an alpha-particle scattered by a single nucleus
is enough. Alpha particles are nuclei of helium atoms and, therefore, carry two units,2e, of
positive charge and have the mass of the helium atom. The charge of the gold nucleus is
Ze, where Z is the atomic number of the atom; for gold Z = 79. Since the nucleus of gold is
about 50 times heavier than α-particle, it is reasonable to assume that it remains stationary
throughout the scattering process. Under these assumptions, the trajectory of an alpha-
particle can be computed employing Newton’s second law of motion and the Coulomb’s
law for electrostatic force of repulsion between the alpha-particle and the positively
charged nucleus.
Q2. Why the nucleus of gold is about remains stationary throughout the scattering
process?
a) Because its mass is 100 times the mass of proton.
b) Because its mass is 50 times the mass of proton.
c) Because its mass is 150 times the mass of proton.
d) Because its mass is 200 times the mass of proton.
Q3. Why electrons around the gold nucleus were unable to deflect α particles?
a) Size of α particle is much greater than that of electron.
b) Number of electrons around gold nucleus is very small
c) α particles is much heavier than electron.
d) Electrons are negatively charged.
Physics / XII (2020-21)
Answer : Q1 – a; Q2 – d; Q3 – c; Q4 – a
Q3. From Fig. shown predict which series has waves of maximum frequency
a) Lymen
b) Balmer
c) Paschen
d) Bracket
Q4. What is the maximum energy of photon in emission spectrum of hydrogen atom
a) 13.6 eV
b) 1.36 eV
c) 1.5 eV
d) 1eV
Answer : Q1 – c; Q2 – b; Q3 – a; Q4 – a
Physics / XII (2020-21)
UNIT-IX
ELECTRONIC DEVICES
Two statements are given – One labeled assertion (A) and other labeled reason (R).
Select the correct answer to these questions from the codes (a), (b), (c) and (d) as
given below:
a) Both A and R are true and R is the correct explanation of A
b) Both A and R are true but R is not the correct explanation of A.
c) A is true but R is false.
d) A is false but R is true.
3. Rectifiers :
A semiconductor device is used as a rectifier that allows the voltage to flow in positive
direction and very small value in the reverse direction. Now a days, there is a problem
of supply of less voltage that damages the household appliances.
Q (1). In the depletion region of a diode
a. There are no mobile charges
b. Equal number of holes and electrons exist, making the region neutral.
c. Recombination of holes and electrons has taken place.
d. Immobile charge ions exist.
Q(2).When a p-n junction diode is reverse biased then
a. No Current flows
b. The depletion reason is increased
c. The depletion reason is reduced
d. Height of potential barrier is reduced
Q(3). Diode is used as
a. Oscillator
b. Amplifier
c. Rectifier
d. Modulator
Q(4).Which one statement is incorrect?
a. Diode is used as rectifier
b. Diode is used as half wave rectifier
c. Diode is used as Amplifier
d. Diode is used as full wave rectifier
Answers:
1. (d)
2. (b)
3. (c)
4. (c)
4. Zener diode :
Zener diode is a specially designed p-n junction diode in which both p- side and
n- side of p-n junction are heavily dopped. The zener diode is designed specially to
operate in the reverse break down voltage region continuously without being
damaged. Zener diode is used to remove the fluctuations from given voltage and
thereby provides a voltage of constant magnitude (i.e. zener diode is used as
voltage regulator).
Q (1). Zener diode is mostly used as
a. Half wave rectifier
b. Full wave rectifier
c. Voltage regulator
d. LED
Physics / XII (2020-21)
Q (2). Zener diode is designed to specially work in which region without getting
damaged ?
a. Active region
b. Break down region
c. Forward Biased
d. Reverse biased
Q (3). The depletion region of the zener diode is
a. Thick
b. Normal
c. Very thin
d. Very thick
Q (4). What is the level of dopping in zener diode?
a. Lightly dopped
b. Heavily dopped
c. Moderately dopped
d. No dopping
Answers:
1. (c)
2. (b)
3. (c)
4. (b)
Class: XII Session: 2020-2021
Subject: Physics
Sample Question Paper (Theory)
General Instructions:
(1) All questions are compulsory. There are 33 questions in all.
(2) This question paper has five sections: Section A, Section B, Section C, Section D and
Section E.
(3) Section A contains ten very short answer questions and four assertion reasoning
MCQs of 1 mark each, Section B has two case based questions of 4 marks each,
Section C contains nine short answer questions of 2 marks each, Section D contains
five short answer questions of 3 marks each and Section E contains three long answer
questions of 5 marks each.
(4) There is no overall choice. However internal choice is provided. You have to attempt
only one of the choices in such questions.
Sr. Marks
No.
Section – A
All questions are compulsory. In case of internal choices, attempt
any one of them.
OR
Give the ratio of velocity of the two light waves of wavelengths 4000Å and
8000Å travelling in vacuum.
Page 1 of 10
4 A solenoid with N loops of wire tightly wrapped around an iron-core is 1
carrying an electric current I. If the current through this solenoid is reduced
to half, then what change would you expect in inductance L of the solenoid.
OR
7 In decay of free neutron, name the elementary particle emitted along with 1
proton and electron in nuclear reaction.
OR
OR
For question numbers 11, 12, 13 and 14, two statements are given-one
labelled Assertion (A) and the other labelled Reason (R). Select the
correct answer to these questions from the codes (a), (b), (c) and (d)
as given below.
Page 2 of 10
11 Assertion(A) : 1
In a nonuniform electric field, a dipole will have translatory as well as
rotatory motion.
Reason(R):
In a nonuniform electric field, a dipole experiences a force as well as
torque.
12 Assertion(A): 1
Electric field is always normal to equipotential surfaces and along the
direction of decreasing order of potential
Reason(R):
Negative gradient of electric potential is electric field.
13 Assertion (A): 1
A convex mirror cannot form real images.
Reason (R):
Convex mirror converges the parallel rays that are incident on it.
14 Assertion(A): 1
A convex lens of focal length 30 cm can’t be used as a simple microscope
in normal setting.
Reason (R):
For normal setting, the angular magnification of simple microscope is
M=D/f
Section – B
Questions 15 and 16 are Case Study based questions and are
compulsory. Attempt any 4 sub parts from each question. Each
question carries 1 mark.
15 Faraday Cage: 4
Page 3 of 10
1. Which of the following material can be used to make a Faraday
cage?
(i)
a) Plastic
b) Glass
c) Copper
d) Wood
Page 4 of 10
The total internal reflection of the light is used in polishing diamonds to
create a sparking brilliance. By polishing the diamond with specific cuts, it
is adjusted the most of the light rays approaching the surface are incident
with an angle of incidence more than critical angle. Hence, they suffer
multiple reflections and ultimately come out of diamond from the top. This
gives the diamond a sparking brilliance.
2. The critical angle for a diamond is 24.4o. Then its refractive index is-
a) 2.42
b) 0.413
c) 1
d) 1.413
Page 5 of 10
The brilliance of diamond in the second diamond will be:
Section – C
All questions are compulsory. In case of internal choices, attempt
anyone.
17 Two straight infinitely long wires are fixed in space so that the current in the 2
left wire is 2 A and directed out of the plane of the page and the current in
the right wire is 3 A and directed into the plane of the page. In which
region(s) is/are there a point on the x-axis, at which the magnetic field is
equal to zero due to these currents carrying wires? Justify your answer.
18 Draw the graph showing intensity distribution of fringes with phase angle 2
due to diffraction through single slit.
OR
What should be the width of each slit to obtain n maxima of double slit
pattern within the central maxima of single slit pattern?
OR
20 Explain with help of circuit diagram, the action of a forward biased p-n 2
junction diode which emits spontaneous radiation. State the least band gap
energy of this diode to have emission in visible region.
Page 6 of 10
21 A coil of wire enclosing an area 100 cm2 is placed with its plane making an 2
angle 600 with the magnetic field of strength 10-1T. What is the flux through
the coil? If magnetic field is reduced to zero in 10-3 s, then find the induced
emf?
23 Draw the energy band diagram when intrinsic semiconductor (Ge) is doped 2
with impurity atoms of Antimony (Sb). Name the extrinsic semiconductor so
obtained and majority charge carriers in it.
Section -D
All questions are compulsory. In case of internal choices, attempt
any one.
26 A rectangular loop which was initially inside the region of uniform and time 3
- independent magnetic field, is pulled out with constant velocity 𝑣 as shown
in the figure.
Page 7 of 10
a) Sketch the variation of magnetic flux, the induced current, and
power dissipated as Joule heat as function of time.
OR
b) If, deuterons and alpha particle are accelerated through same potential,
find the ratio of the associated de-Broglie wavelengths of two.
OR
Page 8 of 10
29 Derive an expression for the frequency of radiation emitted when a 3
hydrogen atom de-excites from level n to level (n – 1). Also show that for
large values of n, this frequency equals to classical frequency of revolution
of an electron.
Section – E
All questions are compulsory. In case of internal choices, attempt
any one.
31 a) State Gauss’s law in electrostatics. Show that with help of suitable figure 5
that outward flux due to a point charge Q, in vacuum within gaussian
surface, is independent of its size and shape.
b) In the figure there are three infinite long thin sheets having surface
charge density +2σ, -2σ and +σ respectively. Give the magnitude and
direction of electric field at a point to the left of sheet of charge density
+2σ and to the right of sheet of charge density +σ.
Page 9 of 10
OR
OR
Page 10 of 10
As Per Revised
CBSE Curriculum
2023-24
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