# CBSE Board Class 12 Physics Previous Year Question Papers 2009

## CBSE Board Previous Year Question Papers 2009 for Class 12 Physics

General Instructions:
1. All questions are compulsory.
2. There is no overall choice. However, an internal choke has been pro vided in one
question of two marks, one question of three marks and all three questions of five marks.
You have to attempt only one of the chokes in such questions.
3. Question numbers 1 to 5 are very short answer type questions, carrying on 5one mark each.   e
4. Question numbers 6to 12  are short answer type questions, carrying t two marks each.   twotwo
5. Question numbers 13 to 24are also short answer type questions, carrying tthree marks  hree
each.
6. Question numbers 25 to 27  are long answer type questions, carrying five marks each.
7. Use of calculators is not permitted. However, you may use log tables, if necessary.
8. You may Use the following values of physical constants wherever necessary:
PHYSICS 2009

Q1. . An electrostatic field line cannot be discontinuo . .  us. Why?

Q2. . Two wires of equal lengths are bent in the form o . .  f two loops. One of the loops is square
shaped whereas the other loop is circular. These are suspended in a uniform magnetic field
and the same current is passed through them. Which loop will experience greater torque? Give
reasons.

Q3. . A bulb and a capacitor are connected in series to . .  an a.c. source of variable frequency.
How will the brightness of the bulb change on increasing the frequency of the a.c. source?
Give reason.

Q4. . Ultraviolet light is incident on two photosensiti . .  ve materials having work functions W1 and
W2 (W1 > W2), in which case will the kinetic energy of the emitted electrons be greater? Why?

Q5. . What is the function of cladding' in a typical op . .  tical fiber?

Q6. . Define electric field intensity. Write its S. l u . .  nit. Write the magnitude and direction of
electric field intensity due to an electric dipole of length 2a at the mid- point of the tine joining
the two charges.

Q7. . A parallel capacitor is to be designed with a vol . .  tage rating 1 kV using a material of
dielectric constant 3 and 4ickeclric strength about 10 7 Vm -1 . For safety we would like the
field never to exceed say, 10% of the dipole strength. What minimum area of the plats is
required to have a capacitance of 50 PF?
Or A  capacitor is charged by a 200 V supply. The supply is then disconnected and the
charged capacitor is connected to another uncharged 2  c capacitor. How much
electrostatic energy of the first capacitor is lost in the process of attaining the steady situation?

Q8. . How does the receptivity of (i) a conductor and ( . .  ii) a semiconductor vary with temperature?
Give reason for each case.

Q9. . Write two characteristic properties to distinguis . .  h between diamagnetic and paramagnetic
materials.

Q10. . A circular coil of radius 8 cm and 20 turns rotat . .  es about its vertical diameter with an
angular speed of 50 s-1 in a uniform horizontal magnetic field of magnitude 3 x 10-2 T. Find the
maximum and average value of the emf induced in the coil.

Q11. . State the condition under which the phenomenon of . .  resonance occurs in a series LCR
circuit. Plot a graph showing variation of current with frequency of a.c. source in a series LCR
circuit.

Q12. . A right-angled crown glass prism with critical an . .  gle 41 0 is placed before an object PQ, in
two positions as shown in the figures (i) and (ii). Trace the paths of the rays from P and Q the
prisms in the two cases.

Q13. . State Gauss' theorem. Apply this theorem to obtai . .  n the expression for the electric field
intensity at a point due to an infinitely long, thin, uniformly charged straight wire.

Q14. . Two cells of emf 1.5 V and 2 V and internal resis . .  tance 1 ohm and 2 ohm respectively are
connected in parallel to pass a current in the same direction through an external resistance of
5 ohm.
(i) Draw the circuit diagram.
(ii) Using Kirchhoff's laws, calculate the current through each branch of the circuit and potential
difference across the 5 ohm resistor.

Q15. . What is See beck effect? Plot a graph showing the . .  variation of thermo emf with
temperature of the hot junction (keeping the cold junction at 0 o C) of a thermocouple. How will
the (a) neutral temperature and (b) inversion temperature of the thermocouple change when
the temperature of the cold junction is increased?
Or State Faraday's laws of electrolysis. How does one infer from these laws that the charge
per ion of any chemical element (species) is an integral multiple of e, where e is the charge on
an electron?

Q16. . Define self-inductance and give its S. I . unit.  . .  Derive an expression for self- inductance of
a long, air-cored solenoid of length l, radius r, and having N number of turns.

Q17. . Name the constituent radiation of electromagnetic . .  spectrum which
(a) Is used in satellite communication.
(b) Is used for studying crystal structure.
(c) Is similar to the radiations emitted during decay of radioactive nuclei?
(d) Has its wavelength range between 390 nm and 770 nm.
(e) Is absorbed from sunlight by ozone layer.
(f) Produces intense heating effect.

Q18. . (a) . .  Draw a labelled ray diagram to show the formation of an image by a compound
microscope. Write the expression for its magnifying power.  (b) How does the resolving power of a compound microscope change, when (i) refractive index
of the medium between the object and the objective lens increases; and (ii) wavelength of the

Q19. . Mention the significance of Davisson-Germer exper . .  iment. An  particle and a proton are
accelerated from rest through the same potential difference V. Find the ratio of de-Broglie
wavelengths associated with them.

Q20. . (a) Draw the energy level diagram showing the emi . .  ssion of  -particles followed by
by a  Co nucleus.
(b) Plot the distribution of kinetic energy of J articles and state why the energy spectrum is
continuous.

Q21. . A radioactive sample contains 2.2 ing of pure  . .  C which has half-life period of 12
seconds. Calculate
(i) The number of atoms present initially.
.(ii) The activity when 5  of the sample will be left.
Q22. . On the basis of the energy band diagrams distingu . .  ish between metals, insulators and
semiconductors.           3

Q23. . Distinguish between analog and digital communicat . .  ion. Write any two modulation
techniques employed for the digital data. Describe briefly any one of the techniques used. 33   33

Q24. . A ground receiver station is receiving a signal a . .  t (a) 5 MHz and (b) 100 MHz, transmitted
from a ground transmitter at a height of 300 m located at a distance of 100 km. Identify
whether it is coming via space wave or sky wave propagation or satellite transponder. (Given
the value of radius of the earth is 6400 km and maximum electron density, Nmax = 1012
m-3

Q25. . Explain the principle and working of a cyclotron  . .  with the help of a Labeled diagram. A
cyclotron's oscillator frequency is 10 Mhz. What should be the operating magnetic field for
accelerating protons? If the radius of its 'dees' is 60 cm, what is the kinetic energy of the proton
beam produced by the accelerator? Express your answer in units of Me V.
.       or Depict the magnetic field lines due to two straight, long, parallel conductors carrying
currents 11 and 12 in the same direction. Hence deduce an expression for the force acting per
unit length on one conductor due to the other is this force attractive or repulsive?
Figure shows a rectangular current-carrying loop placed 2 cm away from a long, straight,
current-carrying conductor. What is the direction and magnitude of the net force acting on the
loop?

Q26. . Using Huygen's principle, draw a diagram to show  . .  propagation of a wave-front originating
from a monochromatic point source.
Describe diffraction of light due to a single slit. Explain formation of a pattern of fringes
obtained on the screen and plot showing variation of intensity with angle  in single slit
diffraction.
Or What is meant by a linearly polarized light? Which type of waves can be polarised? Briefly
explain a method for producing polarised light.
Two Polaroids are placed at 900
to each other and the intensity of transmitted light is zero.
What will be the intensity of transmitted light when one more Polaroid is placed between these
two bisecting the angle between them? Take intensity of unpolarised light as I.

Q27. . (a) With the help of a circuit diagram explain th . .  e working of transistor as oscillator.
(b) Draw a circuit diagram for a two input OR gate  and explain its working with the help of
input, output waveforms.
Or (a) Explain briefly with the hell) of a circuit  diagram how V - I characteristics of a p-n
junction diode are obtained in (i) forward bias, and (ii) reverse bias.
(b) A photodiode is fabricated from a semiconductor with a band gap of 2.8 EV. Can it detect
wave length of 6000. nm? Justify.