SUCCESS KEY TEST SERIES

Annual Examination [ MODEL ANSWER ]

Std: 11th Science Subject: Physics Time: 3 Hours
Date : Sample Answer Key Max Marks: 70

Section A ( MCQ & VSA 1 MARKS Questions)

Q.1 Select and write the correct answer: 10
(i) Ans. (b)
(ii) Ans. (d)
(iii) Ans. (c)
(iv) Ans. (a)
(v) Ans. (d)
(vi) Ans. (b)
(vii) Ans. (d)
(viii) Ans. (a)
(ix) Ans. (a)
(x) Ans. (c)
E = 1.8 × 10³ V/m, d = 3.6 mm = 3.6 × 10⁻³ mm
V = E d = 1.8 × 103 × 3.6 × 10⁻³
V = 6.48 V

Q.2 Answer the following: 8

(i) Ans. The velocity vector of a stationary particle is a zero vector.
(ii) Ans. Displacement = Final position – Initial position
= 10 m – 5 m = 5 m
Velocity = Displacement / Time
= 5 m / 5 s = 1 m/s
(iii) Ans. The principle of conservation of linear momentum states that the total momentum of an isolated
system is conserved during ay interaction.
(iv) Ans. The initial and final velocities of the bodies get exchanged when two bodies of equal masses
undergo elastic head on collision, i.e.
v₁= u₂ and v₂= u₁
(v) Ans. The object feels heavier in a lift which has a net acceleration in the upward direction.
(vi) Ans. The triple point is the temperature and pressure at which solid, liquid, and vapour phases of a
particular substance coexist in equilibrium.
(vii) Ans. The characteristic of sound which is determined by the value of frequency
(viii) Ans. Resistivity of a conductor is numerically the resistance per unit length, and per unit area of cross
section of material of the conductor.

Section B (SA I - 2 MARKS EACH)

Attempt any Eight: 16
Q.3 Ans. (i) No, the answers will not be the same.
(ii) This is because the least count of a metre scale is 0.1 cm, so the probability of systematic error is
high.

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Q.4 Ans.

Q.5 Ans.

Q.6 Ans. The acceleration due to gravity decreases with increase in altitude of the body from the surface of
the Earth.

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Q.7 Ans.

Q.8 Ans.

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Q.9 Ans. (i) Convex mirrors forms diminished images of the object irrespective of the position of the object.
(ii) Concave mirror can form a magnified image as well as diminished image depending on the
position of the object.

Q.10 Ans.

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Q.11 Ans.

Q.12 Ans. 1. In both cases we get two magnets, each having north and south pole.
2. Transverse to it's length: magnetic strength remains same but length become half,
3. Along its length: length remains same but magnetic strength becomes half
Q.13 Ans.

Q.14 Ans.

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 Section C (SA II - 3 MARKS EACH)
Attempt any Eight: 24
Q.15 Ans.

Q.16 Ans. (i) Instantaneous velocity = dx/dt

(ii) Instantaneous acceleration = d²x/dy²
Explanation:
The motion of an object is described by x = f (t)
We have to find the instantaneous velocity and acceleration
Instantaneous velocity = dx/dt
Therefore, Instantaneous velocity = dx/dt = df(t)/dt= f (t)
Hence Instantaneous velocity = f(t)
Acceleration, a = d²x/dy²
Substitute the values, then we get
a = d² f (t)/dt² = f”(t)
Hence, acceleration = f”(t)
Q.17 Ans. 1. There are situations where Newton’s law cannot be applied.
2. Newton’s laws are applicable only in the inertial frames of reference. If the body is in a frame of
reference of acceleration (a), we need to use a pseudo force F = ma in addition to all the other forces
while writing the force equations.
3. Newton’s laws are applicable for point objects and rigid bodies.
4. For objects moving with speeds comparable to that of light, Newton’s laws of motion do not give
results that match with the experimental results and Einstein special theory of relativity has to be
used.
5. Behaviour and interaction of objects having atomic or molecular sizes cannot be explained using
Newton’s laws of motion, and quantum mechanics has to be used.
Q.18 Ans.

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Q.19 Ans.

Q.20 Ans. (i) Radiation is the transfer of heat energy from one place to another via emission of EM energy.
(ii) All objects possess thermal energy due to their temperature.
(iii) The rapidly moving molecules of a hot body emit EM waves travelling with a velocity of light.
(iv) These are called thermal radiations.
(v) These carry energy with them and transfer it to a low-speed molecules of a cold body on which
they fall.
(vi) This results in an increase in the molecular motion of the cold body and its temperature rise.
(vii) Thus the transfer of heat energy by radiation is a two-fold process.

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Q.21 Ans.

Q.22 Ans. A wave in which the particles of a medium vibrate in a direction perpendicular to the direction of
propagation of the wave is called a transverse wave.
Characteristics of transverse waves:
(i) All the particles of the medium vibrate perpendicular to the direction of propagation of the wave.
(ii) The medium is divided into alternate crests and troughs when a transverse wave propagates
through the medium.
(iii) A crest and an adjacent trough form one complete cycle of transverse waves.
(iv) Crests and troughs traverse in a medium and are responsible for energy propagation in a
medium.
(v) Transverse waves can travel through solids and on the surface of the liquids only.
(vi) There is no change in pressure and density as the transverse wave propagates through the
medium.
(vii) Transverse waves can be polarized.
(viii) Medium conveying a transverse wave must possess elasticity of shape.
Q.23 Ans.

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Q.24 Ans.

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Q.25 Ans. Radio waves are produced by accelerated motion of charges in a conducting wire. The frequency of
waves produced by the circuit depends upon the magnitudes of the inductance and the capacitance.
Thus, by choosing suitable values of the inductance and the capacitance, radio waves of desired
frequency can be produced.
Uses :
1) Radio waves are used for wireless communication purpose.
2) They are used for radio broadcasting and transmission of TV signals.
3) Cellular phones use radio waves to transmit voice communication in the ultra high frequency
(UHF) band.
Q.26 Ans. 1. Consider a p-type semiconductor connected to terminals of a battery. When the circuit is
switched on, electrons are attracted to the positive terminal of the battery and occupy nearby holes.
This generates holes at the positions which were previously occupied by electrons.
2. Similarly, electrons at other positions also move towards the positive terminal and create holes in
the positions they occupied previously. Finally the hole is captured at the negative terminal by the
electron supplied by the battery at that end.
3. This keeps the density of holes constant and maintains the current so long as the battery is
working. Thus, physical transportation is of the electrons only.
4. However, it feels like the holes are moving towards the negative terminal of the battery. Positive
charge is attracted towards negative terminal. Thus holes, which are not actual charges, behave like
a positive charge.
5. In this case, there is an indirect movement of electrons and their drift speed is less than that in the
n-type semiconductors. The mobility of holes is less than that of the electrons which lead to less
conductivity.
Section D (SA II - 4 MARKS EACH)
Attempt any Three: 12
Q.27 Ans. (i) (a) The relative error represented by percentage (i.e., multiplied by 100) is called the percentage
error.
(b) The ratio of the mean absolute error in the measurement of a physical quantity to its arithmetic
mean value is called relative error.
(ii)

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Q.28 Ans.

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Q.29 Ans. (i) 1. The ability of an optical material to disperse the constituent colors is known as the dispersive
power.
2. It is measured for any two colors as the ratio of the angular separation to the mean deviation for
those two colors.
(ii)

Q.30 Ans. Consider a potential difference V applied between two parallel plates separated by a distance ‘d’.
The electric field between them directed from plate A to plate B as shown.

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 If we move the charge +q from the negative plate B to the positive plate A, the work done against
the field is W = Fd
The potential difference V between the two plates is given by
W = Vq, but W = Fd
Vq = Fd
F/q = V/d = E
Thus the electric field between the plates is given by,
E = V/d
Normally the value of d will be very small so that even a small voltage can produce a reasonably
large electric field.

Q.31 Ans. (i) 1. Magnetic lines of force originate from the north pole and end at the south pole.
2. The magnetic lines of force of a magnet or a solenoid from closed loops. This is in contrast to the
case of an electric dipole, where the electric lines of force originate from the positive charge and end
on the negative charge.
(ii)

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