DELHI PRIVATE SCHOOL – DUBAI HY 12 PH MN 2023-24

HALF YEARLY EXAMINATION SAMPLE PAPER MAX MARKS: 70 marks

PHYSICS TIME: 3 Hrs.
GRADE-XII
General Instructions: -
 There are 33 questions in all. All questions are compulsory.
 This question paper has five sections: Section A, Section B, Section C, Section D and
Section E.
 All the sections are compulsory.
 Section A contains sixteen questions, twelve MCQ and four Assertion Reasoning based
of 1 mark each, Section B contains five questions of two marks each, Section C
contains seven questions of three marks each, Section D contains two case study
based questions of four marks each and Section E contains three long answer
questions of five marks each.
 There is no overall choice. However, an internal choice has been provided in one
question in Section B, one question in Section C, one question in each CBQ in Section
D and all three questions in Section E. You have to attempt only one of the choices in
such questions.
 Use of calculators is not allowed.
 You may use the following values of physical constants where ever necessary

SECTION A
1. Two charged spheres A and B having their radii in the ratio 1: 2 are connected 1
together with a conducting wire. The ratio of their surface charge densities σ A/ σB will
be
a) 1:2 b) 2:1 c) 1:4 d) 4:1
2. Two point charges +16 q and -4q are located at x=0 and x=L. The location of the 1
point on the x axis at which the resultant electric field due to these charges is zero,
is:
a) 8L b) 6L c) 4L d) 2L
3. An electric dipole placed in a uniform electric field will experience: 1
a) only a force b) only a torque
c) both force and torque d) neither force nor torque
4. A charge Q is located at the centre of a circle of radius r. The work done in moving a 1
test charge q0 from point A to point B (at opposite ends of diameter AB) so as to
complete a semicircle is [k=1/ (4πε0)]

1
 q0
a) k Q b) Q q 0/ r2 c) kq 0 Qr d) zero
r

5. 64 drops each having the capacity C and potential V are combined to form a big 1
drop. If the charge on the small drop is q, then the charge on the big drop will be
a) 2q b) 4q c) 16q d) 64q

6. Two capacitors of capacitance 6 µF and 4 µF are put in series across a 120 V 1

battery. What is the potential difference across the 4 µF capacitor?
a) 72 V b) 60 V c) 48 V d) zero
7. Which of the following characteristics of electrons determines the current in a 1
conductor?
a) Drift velocity alone b) Thermal velocity alone
c) Both drift velocity and thermal velocity d) Neither drift nor thermal velocity
8. The following figure represents a balanced Wheatstone 1
bridge circuit. What is the value of X?
a) 15 Ω
b) 20 Ω
c) 25 Ω
d) 30 Ω
9. Biot–Savart law indicates that the moving electrons(velocity v) produces a magnetic 1
field B such that
a) B perpendicular to v b) B parallel to v
c) It obeys inverse cube law d) it is along the line joining the electron
and point of observation

10. An electron is projected with uniform velocity along the axis of a current carrying long 1
solenoid. Which of the following is true?

a) electron will be accelerated along the axis

b) Electron path will be circular about the axis.
c) the electron will experience a force at 450 to the axis and hence execute a helical
path
d) The electron will continue to move with uniform velocity along the axis of the
solenoid
11. A circular current loop of magnetic moment M is in an arbitrary orientation in an 1
external magnetic field B. The work done to rotate the loop by 30° about an axis
perpendicular to its plane is

(a) MB
(b) √3MB/2
(c) MB/2
(d) zero

12 The strength of magnetic field at the center of circular coil is 1

a) µ0 I/2πr
b) µ0 I/2r
2
 c) µ0 I/4πr
d) 2µ0 I/2πr

For Q.13-16
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 and 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
13 A: When a body is charged, its mass changes. 1
R: Charge is quantized
14 A: If electric flux over a closed surface is negative then the surface encloses net 1
negative charge.
R: Electric flux is independent of the charge distribution inside the surface.
15 A: When an electric dipole is placed in uniform electric field, net force on it will be 1
zero.
R: Force on the constituent charges of the dipole will be equal and opposite when it
is in uniform electric field.
16 A: The potential difference between two concentric spherical shells depends only on 1
the charge of inner shell.
R: The electric field in the region in between two shells depends on the charge of
inner shell and electric field is the negative of potential gradient.
SECTION B
17 A heating element using nichrome connected to a 230 V supply draws an initial 2
current of 3.2 A which settles after a few seconds to a steady value of 2.8 A. What is
the steady temperature of the heating element if the room temperature is 27.0 °C
and the temperature coefficient of resistance of nichrome is 1.70 × 10–4 °C–1?
OR
When 5V potential difference is applied across a wire of length 0.1m the drift speed
of electrons is 2.5×10-4 m/s. If the electron density in the wire is 8×1028 m-3, calculate
the resistivity of the material of wire
18 A sheet of Aluminum foil of negligible thickness is placed between the plates of a 2
capacitor. What effect has it on the capacitance if
i) the foil is electrically insulated from the plates and
ii) the foil is connected to the upper plate with a conducting wire.

19 Three identical dipoles are arranged as shown below. What will be the net electric 2
field at P (𝑘 = 1/ 4𝜋𝜀0 ).

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20 Two parallel plate capacitors X and Y have the same area of 2
plates and same separation between them. X has air between
the plates while Y contains a dielectric medium εr = 4.
Calculate the capacitance of each capacitor if equivalent
capacitance of the combination is 4 µF.

21 Electric field intensity at point B due to a point charge Q kept at point A is 24 N/C 2
and the electric potential at point B due to the same charge is 12J/C. Calculate the
distance AB and the magnitude of charge Q
SECTION C
22 Two large thin metal plates are parallel and close to each other. On their inner faces, 3
the plates have surface charge densities +σ and of magnitude 17.0 × 10−22 C/m2.
Find the Electric field: (a) in the outer region of the first plate,
(b) in the outer region of the second plate,
(c) between the plates?
23 3

You are given an air filled parallel plate capacitor C1. The space between its plates is
now filled with slabs of dielectric constants K1 and K2 as shown in capacitor C2. Find
the capacitance of the capacitor C2 if the area of the plates
is A, and the distance between the plates is d.

24 Using the Kirchhoff’s laws determine the 3

value of the current I1 in the electric circuit
shown in figure.

25 A storage battery of emf 8 V and internal resistance 0.5 ohm is being charged by d.c 3
supply of 120 V using a resistor of 15.5 ohm
a) Draw the circuit diagram.
b) Calculate the potential difference across the battery.

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 c) What is the purpose of having series resistance in this circuit?
OR

Determine the current drawn from a 12V supply with internal resistance 0.5 Ω by
the infinite network shown in Figure. Each resistor has 1Ω resistance.

26 Two long straight parallel conductors carry steady current I1 and I2 separated by a 3
distance d. If the currents are flowing in the same direction, show how the magnetic field set
up in one produces an attractive force on the other. Obtain the expression for this force per
unit length of the conductor.

27 Two identical circular wires P and Q each of radius R and 3

carrying current ‘I’ are kept in perpendicular planes such that
they have a common centre as shown in the figure. Find the
magnitude and direction of the net magnetic field at the
common centre of the two coils

28 Two insulated charged copper spheres A and B of identical sizes with charges 2q 3
and 3q respectively repel with a force F when placed at a distance d. A third sphere
C of the same size but uncharged is brought in contact with A first and then in
contact with B and finally placed in the middle of both. What is the new force on A?
SECTION D
29 CASE STUDY 1 4

For the various charge systems, we represent equipotential surfaces by curves and
line of force by full line curves. Between any two adjacent equipotential surfaces, we
assume a constant potential difference the equipotential surfaces of a single point
charge are concentric spherical shells with their centers at the point charge. As the
lines of force point radially outwards, so they are perpendicular to the equipotential
surfaces at all points.

1) Which of the following is correct about the property of equipotential surface.

a) Electric field is always parallel to potential surface.

b) It has variable voltages on the surface.

c) Electric field is always perpendicular to potential surface

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 d) None of the above

2) Earth is an equipotential surface because

a) Earth is spherical in shape

b) Earth is a conductor.

c) Earth has electric field

d) None of the above

3) Two points A and B at a distance of 5cm are each at a potential of 10 V.

What will be the work done to move a positive charge of 2 C from A to B.

a) zero

b) 2J

c) 5 J

d) None of the above

3)

The diagram shows regions of equipotential. A positive charge is moved

from A to B in each diagram.

a) Maximum work is required to shift charge in fig B

b) Maximum work is required to shift charge in fig D

c) In all four cases work done is the same.

d) Maximum work is required to shift charge in fig C

30 4
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 CASE STUDY -Wheatstone bridge

Wheatstone bridge is an arrangement of four resistances P, Q, R and S connected

as shown in figure. Their values are so adjusted that the galvanometer G shows no
deflection. The bridge is then said to be balanced when this condition is achieved. In
the setup shown here the points B and D are at the same potential and it can be
shown that
P/( Q) = R/( S).
This is called balancing condition. If any three resistances are known the fourth can
be found. The practical form of Wheatstone bridge is Metre bridge. Using this the
unknown resistance can be determined as
S= (R( 100-l))/( l) where l is the balancing length of the metre bridge
a).In a Wheatstone bridge circuit P= 5Ω, Q= 6Ω, R=10Ω, S=5Ω. What is the value of
additional resistance to be used in series with P in order to balance the bridge.
a) 9Ω b) 5Ω c)10Ω d) 7Ω
b). The bridge is more sensitive when
a) When all resistances are small. b) When all resistances are equal
c) When all resistances are unequal d)When resistance P and Q are equal,
but P > R and Q >S
c).When a semiconductor wire connected to right gap of a metre bridge is heated,the
balancing point
a) Shifts towards right b) Shifts towards left
c) Remains unchanged d) Remains at zero
d). The percentage error in measuring resistance with a metre bridge can be
minimized by adjusting the balancing point close to
a) 0 b) 20 cm c) 50 cm d) 80 cm
e). In a meter bridge experiment, the ratio of left gap resistance to right gap
resistance is 3:2. The balance point from left is
a). 20cm b). 50cm c). 40cm d). 60cm
SECTION E
31 a) An electric dipole of dipole moment ⃗p consists of point charges + q and - q 5
separated by a distance 2a apart. Deduce the expression for the electric field⃗ E
due to the dipole at a distance x from the center of dipole on its axial line in terms
of the dipole moment⃗p. Hence show that in the limit x ¿ a , ⃗ E =2 ⃗p / (4πε0x3).
b) Given the electric field in the region ⃗E = 2xi^ , find the
net electric flux through the cube and the charge
enclosed by it.

OR

a) Consider a system of n charges q1, q2 ...... qn with

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 position vectors⃗
r 1,⃗
r 2 … .. ⃗
rn
relative to some origin 'O'. Deduce the expression for the net electric field⃗
E at a
point P with position vector ⃗ r p , due to this system of charges.
b) Five charges q each are placed at the corners of a regular pentagon of side a.

What will be the electric field at O if the charge from one of the corners (say A) is
removed?

32 a) Compare the individual dipole moment and the specimen dipole moment for H2O 5
molecule and O2 molecule when placed in
(i) Absence of external electric field. (ii) Presence of external electric field.
Justify your answer.
b) Given two parallel conducting plates of area A
and charge densities + σ and - σ. A dielectric
slab of constant K and a conducting slab of
thickness d each are inserted in between them
as shown.
(i) Find the potential difference between the
plates.
(ii) Plot E versus x graph, taking x = 0 at
positive plate and x = 5d at negative plate.

OR
a) Derive an expression for the potential at a point P due to a point charge Q which
is at a distance r from the charge.
b) Draw a plot showing the variation of electric field (E) and electric potential (V) with
distance r due to a point charge Q.
33 a) State Biot-Savart’s law and express it in vector form. 5
b) Using Biot-Savart’s law, derive an expression for magnetic field at any point on
axial line of a current carrying circular loop. Hence, find magnitude of magnetic
field intensity at the center of circular coil.

OR
a) Draw a labelled diagram of a moving coil galvanometer. Describe briefly its
principle and working.
b) Answer the following questions
i) Why is it necessary to introduce a cylindrical soft iron core inside the coil of a
Galvanometer.
ii) Increasing the current sensitivity of a galvanometer may not necessarily increase its
voltage sensitivity. Explain, giving reason.

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