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GENERAL INSTRUCTIONS:
DWARKA INTERNATIONAL SCHOOL
SECTOR-12, DWARKA, NEW DELHI-78
Sample Paper
PHYSICS
Class -XII
TIME: 3 hours
(i) All questions are compulsory. There are 26 questions in all.
(ii) This question paper has five sections: Section A, Section B, Section C, Section D and
Section E.
(iii) Section A contains five questions of one mark each, Section B contains five questions of
two marks each, Section C contains twelve questions of three marks each, Section D contains
one value based question of four marks and Section E contains three questions of five marks
each.
(iv) There is no overall choice. However, an internal choice has been provided in one question of
two marks, one question of three marks and all the three questions of five marks weightage.
You have to attempt only one of the choices in such questions.
(v) You may use the following values of physical constants wherever necessary:
c = 3 × 108 m/s
h = 6.63 × 10–34 Js
e = 1.6 × 10–19 C
µ0 = 4π × 10–7 T m A–1
ε 0 = 8.854 × 10–12 C2 N–1 m–2
Section A
1. What is the value of the angle between the vectors 𝑝⃗ and 𝐸⃗ for which the
potential energy of an electric dipole of dipole moment 𝑝⃗ , kept in an external
electric field 𝐸⃗ , has maximum value.
2. State which of the two, the capacitor or an inductor, tends to become a
SHORT when the frequency of the applied alternating voltage has a very high
value.
3. How are X-rays produced?
4. Write the mathematical form of the law which is a statement of the fact that
magnetic monopoles do not exist.
5. The sum of two points charges is 7mC . They repel each other with a force of 1
N when kept 30 cm apart in free space. Calculate the value of each charge.
Section B
6. Calculate the value of the unknown potential V for
the given potentiometer circuit. The total length (400
cm) of the potentiometer wire has a resistance of 10
Ω and the balance point is obtained at a length of 240 cm.
7. What is the principle of working of transformer? Describe. Does a transformer
violate the principle of energy conservation? Explain. Can a
transformer be used to step up d.c? Explain.
8. Determine the electrostatic potential energy of the square
shape system (side = a) of charges shown in the diagram
below.
9. Define the coefficient of self induction. A coil has an
inductance of 0.03H. Calculate the emf induced when current in the coil
changes at a rate of 200 A/s.
10. State Ampere’s circuital law. Obtain an expression for magnetic field at a
point will inside the current carrying solenoid with neat diagram.
Section C
11. Eight identical spherical drops, each carrying a charge 1 nC are at a potential
of 900 V each. All these drops combine together to form a single large drop.
Calculate the potential of this large drop.
12. Find the value of the phase lag/lead between the
current and voltage in the given series LCR circuit.
Without making any other change, find the value of
the additional capacitor, such that when ‘suitably
joined’ to the capacitor ( C= 2μF) as shown, would
make the power factor of this circuit unity.
13. Identify the part of the electromagnetic spectrum which is : (i) suitable for
radar systems used in aircraft navigation, (ii) produced in nuclear reactions,
(iii) produced by bombarding a metal target target by high speed electrons.
14. Find the frequency of LCR series resonant circuit. Define Q factor and show
that 𝑄 = (1/𝑅)√𝐿/𝐶.
15. A short bar magnet has a magnetic moment of 048J/T.
a. Give the direction and magnitude of the magnetic field produced by
the magnet at a distance of 10 cm from the centre of the magnet on the
equatorial line of the magnet.
b. If this magnet lies aligned with the direction of a uniform magnetic
field of 0.22T. What is the amount of work required by an external
torque to turn the magnet so as to align its magnetic moment normal to
the field direction of field? Calculate the torque experienced by
magnetic dipole in the case.
16. A galvanometer coil has a resistance of 12 Ω and the metre shows fill scale
deflection for a current of 3mA. How will you convert the metre into a
voltmeter of range 0 to 18 V? How much resistance is to be connected in series
with 18 V voltmeter to convert into 24V voltmeter? Justify your answer.
17. Deduce an expression for the capacitance of a parallel plate capacitor when a
conducting slab is inserted between the plates. Assume that the slab thickness
to be less than the plate separation.
18. A 100/μF capacitor in series with a 100Ω resistance is connected to a 200 V –
50 Hz supply.
a. Determine the average power dissipated per cycle of the AC.
b. Determine the current amplitude in the circuit.
c. Determine the time lag between the current maximum and the voltage
maximum.
d. Determine the impedance of the circuit.
19. State the theorem which relates total charge enclosed within a closed surface
and the electric flux passing through it. Prove it for a single point charge.
OR
A Dipole is made up of two charges + q and – q separated by a distance 2a.
Derive an expression for the electric field 𝐸⃗𝑒⃗ due to this dipole at a point
distant r from the centre of the dipole on the equatorial plane.
Draw the shape of the graph, between |𝐸⃗𝑒⃗ | and r when r>>𝑎.
20. State the working principle of the potentiometer. Draw a circuit diagram to
compare the emf’s of two primary cells using potentiometer. Give an
expression for to compare emf’s of two primary cells in terms of balancing
lengths.
21. A capacitor of 20 mF and charged to 500 V is connected in parallel to another
capacitor of 10 mF charged to 200 V. Find the common potential and loss of
energy.
22. A circular coil of radius 8cm and 20 turns rotates about its vertical diameter
with an angular speed of 50 s-1. In uniform horizontal magnetic fields of
magnitude 0.03T. find the maximum and average value of emf induced in the
coil?
Section D (Value Based Question)
23. Nisha joined a PG course in Nanotechnology lab in IIT Chennai. The first day,
when she went to the lab, she met the lab assistant. The lab assistant greeted
her and advised her not to touch the wires which were suspended from the
roof at every part of the lab as they were from high voltage lines. The lab
assistant also told her not to bring any of the two wires closer to each other
during any experimental applications and explained her about the
precautions that have to be taken in the lab.
a. Mention any two values of the lab assistant towards Nisha?
b. Why two high voltage power transmission lines should not be close to
each other?
c. Give an expression for the magnetic force that acts between the wires?
Section E
24. Explain with the help of a diagram the underlying principle, construction and
working of a cyclotron. Discuss the limitation of a cyclotron.
OR
What are Eddy currents? How are they produced? In what sense Eddy
currents are considered undesirable in a transformer? How can they be
minimized? Give two applications of Eddy
current?
25. Explain with diagram, the construction, principle of a moving coil
galvanometer. Prove that the current flowing through the same is directly
proportional to the deletion. What is the importance of radial magnetic field?
OR
Discuss the working of a series LCR circuit. Drive relation for effective
voltage, opposition, current and phase
26. State the law which relates to generation of induced emf in a conductor being
moved in a magnetic field. Apply this law to obtain an expression for the
induced emf when one ‘rod’ of a rectangular conductor is free to move in a
uniform, time independent and ‘normal’ magnetic field.
OR
State the principle and working of an ac generator with labeled diagram.
Draw waveform for a.c.