MOTITHANG HIGHER SECONDARY SCHOOL

THIMPHU THROMDE
“Every child is inspired to learn and empowered with wisdom to excel in life”
MID TERM EXAMINATIONS, 2019

Physics Paper 1 (Theory) Reading Time: 15 mins

Class: XII Writing Time: 3 hours
Date: Full marks: 100
Name: ………………………………… Invigilator’s initial

Roll No. ……… Class: ……… Sec: …..

For Teacher’s Use Only Grand

Section A(40) Section B(60) Total
Question
1a 1b 1c 1d 1e Q2 Q3 Q4 Q5 Q6 Q7 Q8
(15) (5) (5) (5) (10) (10) (10) (10) (10) (10) (10) (10)

Award
Teacher’s
initial
Total
Marks
Awarded

READ THE FOLLOWING DIRECTIONS CAREFULLY:

1. Do not write for the first 15 minutes. This time is to be spent reading the questions
2. After having read the questions, you will be given three hours to answer all questions.
3. Answer all the questions in section A. answer any six questions from section B.
4. All workings, including rough work should be done on the same sheet and adjacent to the rest of
the answer. The intended marks for the questions are given in brackets [ ].
5. A list of useful physical constants is given at the end of the question paper.
6. Remember to write quickly but neatly.

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MHSS/XII-PHY/MT-2019/ST
 Section A (40 marks)
Answer ALL the questions

Question 1
(a) Each question is followed by four possible choices of answers. Choose the correct alternative
and circle it. Do not circle more than one alternative. If there are more than one choices circled,
NO score will be awarded. [15]

(i) Water rises to a height of 16 cm in a capillary tube of height 18 cm above the water level. If
the tube is cut at height of 12 cm,
A water will come as a fountain from the capillary tube.
B water will stay at a height of 12 cm in the capillary tube.
C the height of water in the capillary tube will be 4 cm.
D water will flow down the side of the capillary tube.
(ii) Surface tension is due to
A elastic force. C adhesive force.
B cohesive force. D gravitational force.
(iii)Resonance is a special case of
A forced vibration. C damped vibration.
B natural vibration. D undamped vibration.
(iv) A particle performing S. H. M. passing through mean position has
A maximum potential energy. C minimum kinetic energy.
B maximum kinetic energy. D maximum acceleration.
(v) The period of oscillation of a simple pendulum of constant length at earth’s surface is T. Its
period inside the mine is
A greater than T. C equal to T.
B less than T. D not able to be compared.
(vi) All curves for real gases approach the ideal gas behaviour at
A high temperatures and low C low temperatures and high
pressures. pressures.
B high temperatures and high D low temperatures and low pressures.
pressures.
(vii) Two identical metallic spherical shells A and B having charges + 4Q and -10Q are kept a
certain distance apart. A third identical uncharged sphere C is first placed in contact with
sphere A and then with sphere B. The charge on sphere B is now
A -8Q C 2Q
B -4Q D 4Q
(viii) The charge on any object is always an integral multiple of smallest unit of charge (e) which
is equal to the charge on an electron. This explanation is according to

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MHSS/XII-PHY/MT-2019/ST
 A additive nature of charge. C quantisation of charge.
B conservation of charge. D transfer of electrons.

(ix) The current in a capacitor during charging process

A increases exponentially. C increases linearly.
B decreases exponentially. D decreases linearly.
(x) The capacitors in the given circuit diagram have equal capacitance of 10μF each. What is the
equivalent capacitance between X and Y?
A 50 μF.
B 40 μF. X Y
C 20 μF.
D 10 μF.

(xi) When the north pole of the magnet is pulled away from a metallic ring as shown, the
induced current in the ring will be
A in clockwise direction.
B in anti-clockwise direction.
C first clock-wise then anti-clockwise.
D first anti-clockwise then clockwise.

(xii) An alternating emf is given by E= 200sin (50πt) volt. The rms value of the emf is
A. 200 2 V D. 200V
B. 200 / 2 V
C. 100V
1 1
(xiii) The graph given below shows versus graph for a
v u
concave mirror. Study the graph carefully and answer the
question that follows.
Which of the following combinations are not possible in a
concave mirror?
A Real object and real image.
B Real object and virtual image.
C Virtual object and real image.
D Virtual object and virtual image.

(xiv) The semiconductors having only a single type of atoms as their constituent particles are
A. Extrinsic semiconductors. C. Compound semiconductors.
B. Intrinsic semiconductors. D. Impure semiconductors.
(xv) The loss of energy in a transformer due to humming sound produced by its loose
components is called
A magnetostriction. C copper loss.
B flux leakage. D iron loss.

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MHSS/XII-PHY/MT-2019/ST
 (b) Fill-in-the-blanks with appropriate words. [5]
(i) In simple harmonic motion, the restoring force is directed towards the ______________
position and it is always opposite to the ______________ vector.

(ii) In __________ transformer the number of turns in the secondary windings is more than the
number of turns in the primary windings and it’s based on principle of ______________.

(iii) Kirchhoff’s first law is a statement of law of conservation of _____________ and

Kirchhoff’s second law is a statement of law of conservation of _________________.

(iv) If the angle of contact of a liquid and solid surface is ________ than 90°, then the liquid will
spread on the surface of the solid.

(v) Ideal gas have very ________density.

(vi) Electric flux is a ________ quantity.
(vii) A device which is used to store energy in the form of potential energy in the electric field is
known as a __________________.

(c) Match each item of Column A with the most appropriate item of Column B. Rewrite
the correct pairs by writing the number and the corresponding alphabet in your answer
sheet. [5]

Column A Column B

i. Angular frequency (ω) a. 𝑋𝐿 = 𝑋𝐶

ii. Magnetic flux density b. periodic
iii. Gravitational field lines c. scalar
iv. Capacitors in series d. oscillatory
v. Electric field lines e. superconductor
vi. Impedance f. rad/s
vii. Planetary motion g. same charge
viii. Time constant h. Effective resistance
ix. Resonance i. curved
x. Critical temperature j. vector
k. conservative

l. RC

m. straight

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 Column A Column B

i. Angular frequency (ω)

ii. Magnetic flux density
iii. Gravitational field lines
iv. Capacitors in series
v. Electric field lines
vi. Impedance
vii. Planetary motion
viii. Time constant
ix. Resonance
x. Critical temperature

(d) Correct the following statements. [5]

(i) The bundle of streamlines having the same velocity of the liquid particles over any cross-
section perpendicular to the direction of flow of the liquid is known as laminar flow.
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1 −bt
(ii) The mechanical energy of a damped oscillator is given by KA2e 2m .
2
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(iii) When a dielectric slab is removed from a capacitor, its capacitance increases.
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(iv) An induced emf appears in any coil in which the current is flowing.
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(v) The capacitor blocks the flow of a. c. but provides easy flow of d. c.
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(e) Answer the following questions: [10]

(i) Why do you generally squeeze the garden hose to water the plants? [1]
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(ii) What is free oscillation of a system? [1]

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(iii) Graph below shows the position of a particle executing SHM. When will be the speed of the
particle greatest? [1]

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(iv) What happens to the pressure in a tightly sealed house when the electric furnace turns on and
runs for while? [1]
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(v) An electron and a proton are placed 2 mm apart in air. What is the magnitude of electrostatic
force between them? [2]

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(vi) When a credit card is swiped through a card reader, the information coded in a magnetic
pattern on the back of the card holder is transmitted to the card holder’s bank. Why is it
necessary to swipe the card rather than holding it motionless in the card reader’s slot? [1]
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(vii) A 100 mH inductor is connected to an AC generator with peak voltage of 60 V. What is the
amplitude of the resulting alternating current if the frequency of the emf is 2 KHz? [2]

(viii) Distinguish between capacitor and battery. [1]

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 Section B (60 marks)
Answer any SIX questions
Question 2
(a) Obtain the ideal gas equation, PV = NkT, starting from the expression, PV = nRT. [2]

(b) In the figure, the block has a kinetic energy of 3 J and the spring has an elastic potential
energy of 2 J when the block is at x = + 2.0 cm. When the block is at x = 0, what are the
Kinetic energy, Potential energy and total energy? [2]

(c) The phenomenon of surface tension of liquids is explained by molecular theory. Do you agree
with this theory? Justify your stand. [2]
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(d) Following are the pairs of capacitive reactance and inductive reactance respectively for three
sinusoidal driven series RLC circuits: Circuit 1: 50 Ω and 100 Ω. Circuit 2: 100 Ω and 50 Ω.
Circuit 3:50 Ω and 50 Ω.
In which circuit, does the current (i) Lead the applied emf? (ii) Lag the applied voltage?
In which circuit, (i)Does an electrical resonance take place? (ii) Current is maximum? [2]

(e) Imagine you are an astronaut, eagerly wanting to know whether there is magnetic field on an
unknown planet or not. How can you detect the presence of magnetic field on the unknown
planet with the help of sensitive galvanometer and a coil of wire? Name the phenomenon. [2]
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Question 3
(a) i. You are to make a resistor by winding a wire around a cylindrical rod. To make the
inductance as small as possible, it’s proposed that you wind half the wire in one direction and
the other half in opposite direction. Would this achieve the desired result? Why or why not?
[1]
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ii. Your teacher gives you a wire and asks you to design a generator. You are asked to make
either one turn square coil or two turn square coil with the given wire. Which one would
you choose to produce maximum emf for a given frequency and magnetic field? Why?
[1]
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(b) A parallel plate air capacitor has a circular disc of diameter 0.1 m, 2 mm apart and potential
difference of 300 V is connected between the plates. Calculate: (i) Energy of the capacitor and (ii)
Electric intensity between the plates. [3]

(b) Dorji says that Gravitational field is similar to Electric field. Is his statement correct? Justify.
[2]
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(d) Show graphically how velocity of body in fluid varies with time, both in presence and absence
of drag force. [2]

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(e) The natural frequency of a musical instrument is 256 hertz. When in oscillation, a periodic
force of 257 hertz frequency is applied on it. What will be the effect on the amplitude of the
oscillations? Why? [1]
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Question 4
1 2
(a) Using the expression for kinetic energy, K .E. =
mvrms , derive another expression for kinetic
2
energy for an ideal gas molecule which shows that the energy depends only on absolute
temperature. [2]

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(b) In a series LCR circuit set L= 0 H, R = 200 Ω,C = 15 μF, f = 60 Hz, and eo= 36 V. What are
(i) impedance (ii) phase angle and (iii) current amplitude? [4]

(c) Do you think glass windows will be broken by a distant explosion? Give reason for your
answer. [1.5]
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(d) What is an ideal inductor? Why inductors are generally made up of copper? [1.5]
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(e) You press a cork to close the mouth of a flask full of tea. When you release the force, the cork
slowly slides back out. You take out some tea and slide back the cork. Will it slide out as
before? Name the law that is involved here [1]

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Question 5
(a) The shortest distance travelled by a particle performing simple harmonic motion from mean
position in 2 seconds is equal to 3 / 2 of its amplitude. Find its time period. [2]

(b) Derive Terminal Velocity of a freely falling body in a viscous medium. [3]

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(c) How will the resonance frequency of an LCR series circuit change if we bring the plates of
the capacitor closer? Use proper expressions to support your answer. [2]
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(d) The figure shows two protons (symbol 𝑝) and one electron (symbol 𝑒) on an axis. What is the
direction of:
a) The electrostatic force on the central proton due to the electron
b) The electrostatic force on the central proton due to the other proton, and
c) The net electrostatic force on the central proton? [1.5]

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(e) What is mutual induction? Write the SI unit of mutual inductance. [1.5]
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Question 6
(a) What type of mirror would you prefer in your car for observing traffic at your back? Give two
reasons to support your answer. [1.5]
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(b) The time (t) and displacement (y) relation of a particle executing SHM is given by the
equation y= 0.50 sin (500t+0.5), where distance is in cm and time in second. Calculate the
values of: (i) amplitude (ii)angular frequency (iii) frequency (iv) time period (v) initial phase.
[3]

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(c) Using a potential divider circuit diagram, explain how the output voltage is varied in light and
dark. [2]

(e) The charge on the charging capacitor in RC circuit which varies with time is given by
𝑞𝑜 (1 −e-(t/RC) ). From this equation derive the current across the charging capacitor which
varies with time. [2]

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(f) Ten oxygen molecules are moving with the following speeds: four at 200m/s, two at 500 m/s
and four at 600 m/s. Calculate their rms speed. [1.5]

Question 7
(a) Why do addition of flux makes soldering easier? [1]
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(b) Is there a possibility of room temperature superconductors (RTS) in the near future? Support
your answer with two reasons. [1.5]

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(c) Draw ray diagram of an image formed by a shaving mirror. [1.5]

(d) Derive the expression of self-inductance of a solenoid. [3]

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(e) Calculate the equivalent capacitance of the network shown below between the points ‘A’ and ‘B’,
Given: C=1 C=2 12 µ F , C3 = 7 µ F , C=
4 C=
5 C=6 15µ F [3]

A
C1 C4
C3 C5

B C2 C6

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Question 8
(a) Using Kirchhoff’s laws, find currents I1 I2 and I3 in the network below [3]

(b) Two coils, coil A and coil B are at fixed locations. When coil A has no current and the
current in coil B increases at the rate of 15.0 A/s, the emf in coil A is 25.0 mV.
(i) What is the mutual inductance of the two coils?
(ii) When coil B has no current and coil A has a current of 3.6 A, what is the flux linkages in
coil B? [3]

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(c) Derive the mirror equation. [3]

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(d) Dorji is swinging on a swing in the sitting position. How will the period of the swing change
if he stands up? [1]

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PHYSICAL CONSTANTS AND RELATIONS

Acceleration due to gravity g = 9.8 m/s2
Avogadro’s number NA = 6.022 × 1023
Boltzmann constant k =1.38 × 10-23 J/K
Density of water at 4˚C ρ =1000 kg/m3
Electron charge e = 1.6 × 10-19 C
Energy equivalent of 1u = 931.5 MeV
Mass of an electron me = 9.1 × 10-31 kg
Mass of a neutron mn = 1.008665 u
Mass of a proton mp = 1.007276 u
Permeability of free space μ0 = 4π × 10-7 TmA-1
Permittivity of free space ɛ0 = 8.85 ×10-12 C2N-1m-2
Speed of electromagnetic wave c = 3 × 108 ms-1
Standard atmospheric pressure 1 atm = 101325 Pa
Universal gas constant R = 8.31 J/mol.K
1 electron volt 1eV = 1.6 × 10-19 J
π = 3.14
ɛ0 = 8.85 ×10-12C2N-1m-2
μ0 = 4π × 10-7 TmA-1
π = 3.14

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