CBSE Question Paper 2009 for Class 12 - Physics (Theory)

by saumil shrivastava

General Instruction for CBSE question Paper

(i) All the questions are compulsory

(ii) There are 30 Questions in total. Questions 1 to 8 carry one mark each, questions 9 to 18 carry two marks each, questions 19 to 27 carry three marks each and questions 28 to 30 carry five marks each.

(iii) There are no overall choice. However, an internal choice has been provided in one question of two marks, one question of three marks and all three questions of five marks each. You have to attempt only one of the choices in such questions.

(iv) Use of calculators is not permitted.

(v) You may use the following values of physical constants wherever necessary :

$C = 3 \times 10^8\ ms^{-1} /$

$h = 6.626 \times 10^{-34} Js$

$e = 1.602 \times 10^{-19}\ C$

$\mu_{\circ} = 4\pi \times 10^{-7} T\ m\ A^{-1}$

$\cfrac{1}{4\pi \varepsilon_{\circ}} = 9 \times 10^9\ N\ m^2\ C^{-2}$

Mass of electron $m_e = 9.1 \times 10^{-31}\ kg$

Mass of neutron $m_n \cong\ 1.675 \times 10^{-27} kg$

Boltzmann's constant $k = 1.381 \times 10^{-23]\ J\ K^{-1}$

Avogadro's number $N_A = 6.022 \times 10^{23}\ /\ mol^{-1}$

Radius of earth = 6400 km

1. What is the electrostatics potential due to an electric dipole at an equatorial point ?

2. Name the EM waves used for studying crystal structure of solids. What is its frequency range ?

3. An electron does not suffer any deflection while passing through a region of uniform magnetic field. What is direction of the magnetic field ?

4. How would the angular separation of interference fringes in Young's double slit experiment change when the distance between the slit and screen is doubled ?

5. Two thin lenses of power + 6 D and -2 D are in contact. What is the focal length of the combination ?

6. the stopping potential in an experiment on photoelectric effect is 1.5 V. What is the maximum kinetic energy of the photoelectrons emitted ?

7. Two nuclei have mass number in the ratio 1 : 8. What is the ratio of their nuclear radii ?

8. Give the logic symbol of NOR gate.

9. Draw 3 equipotential surfaces corresponding to field that uniformly increase in magnitude but remain constant. along Z-direction. How are these surfaces different from that of a constant electric field along Z-direction ?

10.Define electric flux. Write its S.I unit.

A charge q is enclosed by a spherical surfaces of radius R. If the radius is reduced to half, how would the electric flux through the surfaces chnage ?

11. Define refractive index of a transportation medium.

A ray of light passes through a triangular prism. Plot a graph showing the variation of the angle of deviation with the angle of incidence.

12. Calculate the current drawn from the battery in the given network.

13. Answer the following questions :

(a) Optional and radio telescope are built on the ground while X-ray astronomy is possible only from the satellites orbiting the Earth. Why ?

(b) The small ozone layers on top of the stratosphere is crucial for human survival. Why ?

14. Define current sensitivity and voltage sensitivity of a galvanometer. Increasing the current sensitivity may not necessarily increase the voltage sensitivity of a galvanometer. Justify.

15. Define the term 'linearly polarised light'.

when does the intensity of transmitted light become maximum, when a polaroid sheet is rotated between two crossed polaroids ?

16. A wire of 15 $\Omega$ resistance is gradually stretched to double its original length. It is then cut into two equal parts. these parts are then connected in parallel across a 3-0 volt battery. Find the current drawn from the battery.

17. (a) the mass of a nucleus in its ground state is always less than the total mass of its constituents - neutrons and protons. Explain.

(b) Plot a graph showing the variation of potential energy of a pair of nucleons as a function of their separation.

18. Write the function of (i) Transducer and (ii) Repeater in the context of the communication system.

Write two factors justifying the need of modulation for transmission of signal.

19. A positive point charge (+q) is kept in the vicinity of an uncharged conducting plate. Sketch electric field lines originating from the point on the surface of the plate.

Derive the expression for the electric field at the surface of a charged conductor.

A parallel plate capacitor is charged by a battery. After some time the battery is disconnected and a dielectric constant K is inserted between the plates. How would (i) the capacitance, (ii) the electric field between the plates and (iii) the energy stored in the capacitor, be affected ? Justify your answer.

20. (i) State the principle of working of a meter bridge.

(ii) In a meter bridge balance point is found at a distance l_1 with resistances R and S as shown in the figure.

When an unknown resistance X is connected in parallel with the resistance S, the balance point shifts to a distance l_2. Find the expression for X in terms of l_1, l_2 and S.

21. (i) State Faraday's law of electromagnetic induction.

(ii) A jet plane is travelling towards west at a speed of 1800 km/h. What is the voltage difference developed between the ends of the wing having a span of 25 m, if the Earth's magnetic field at the location has a magnitude of $5 \times 10^{-4}\ T$ and the dip angle is $30^{^{\circ}}$ ?.

22. In Young's double slit experiment, monochromatic light of wavelength 630 nm illuminates the pair of slits and produces an interference pattern in which two consecutive bright fringes are separated by 8.1 mm. Another source of monochromatic light produces the interference pattern in which the two consecutive bright fringes are separated by 7.2 mm. Find the wavelength of light from the second source.

What is the effect on the interference fringes. If the monochromatic source is replaced by a source of white light ?

23. Draw a schematic arrangement of the Geiger - Marsden experiment. How did the scattering of $\alpha - particles$ by a thin foil of gold provide an important way to determine an upper limit on the size of the nucleus ? Explain briefly.

24. Distinguish between sky wave and space wave propagation. Give a brief description with the help of suitable diagrams indicating how these waves are propagated.

25. With the help of suitable diagram, explain the formation of depletion region in a p-n junction. How does its width change when the junction is (i) forward biased, and (ii) reserve biased ?

26. Give a circuit diagram of a common emitter amplifier using an n-p-n transistor. Draw the input and output waveforms of the signal. Write the expression for its voltage gain.

27. Draw a plot showing the variation of binding energy per nucleon versus the mass number A. explain with this plot the release of energy in the processes of nuclear fission and fusion.

28. Draw a schematic sketch of a cyclotron. Explain briefly how it works and how it is used to accelerate te charged particles.

(i) show that time period of ions in a cyclotron. Explain briefly how it works and how it is used to accelerate the speed and radius of circular path.

(ii) What is response condition ? How is it used to accelerate the charged particles ?

(a) Two straight long parallel conductors carry currents $I_1\ and \ I_2$ in the same direction. Deduce the expression for the force per unit length between them.

Depict the pattern of magnetic field lines around them.

(b) A rectangular current carrying loop EFGH is kept in a uniform magnetic field as shown in the figure.

(i) What is the direction of the magnetic moments of the current loop ?
(ii) When is the torque acting on the loop (A) maximum (B) zero ?

29. (a) What are eddy currents ? Write their two applications.

(b) Figures shows a rectangular conducting loop PQRS in which arm RS of length 'l' is movable. The loop is kept in a uniform magnetic field 'B' directed downward perpendicular to the plane of the loop. The arm RS is moved with a uniform speed 'v'

Deduce an expression for

(i) The emf induced across the arm 'RS',
(ii) The external force required to move the arm, and
(iii) The power dissipated as heat.

(a) State Lenz's law. give one example to illustrate this law. ''The Lenz's Law is consequences of the principle of conservation of energy." Justify this statement.

(b) Deduce an expression for the mutual inductance of two long coaxial solenoids but having different radii and different number of turns.

30. (a)
(i) Draw a labelled ray diagram to show the formation of image in an astronomical telescope for a distant object.
(ii) Write three distinct advantages of reflecting type telescope over reflecting type telescope.

(b) A convex lens of focal length 10 cm is placed coaxially 5 cm away from a concave lens of focal length 10 cm. If an object is placed 30 cm in front of the convex lens, find the position of the final image formed by the combined system.

(a) With the help of a suitable ray diagram, derive the mirror formula for a concave mirror.

(b) The near point of a hypermetropic person is 50 cm from the eye. What is the power of the lens required to enable the person to read clearly a book held at 25 cm from the eye ?

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