# CBSE Board Physics Sample Papers for Class 12

Sample Paper – 2009

Class – XII

Subject – Physics

Based on the new pattern for CBSE board examination 2009

Time allowed : 3 hours Maximum Marks : 70

General Instructions :

(i) All questions are compulsory.

(ii) Question numbers 1 to 8 are very short answer type questions, carrying one mark each.

(iii) Question numbers 9 to 18 are short answer type questions , carrying two marks each.

(iv) Question numbers 19 to 27 are also short answer type questions, carrying three marks each.

(v) Question numbers 28 to 30 are long answer type questions, carrying five marks each.

(vi) Use of calculators is not permitted. However, you may use log tables, if necessary.

(vii) Choices have been provided in one question of 2 marks, one question of 3 marks and all the questions of 5 marks.

Q.1> Differentiate b/w drift current and diffusion current in a p-n junction

Q.2> Give a reason why microwaves are better carriers of signal for long-range transmission than radio waves

Q.3> Give 2 factors by which voltage sensitivity of a moving coil galvanometer can be increased

Q.4> What is the power dissipation in an A.C. circuit in which voltage is V = 300sin(wt + p/2) and I = 5sinwt

Q.5> Draw the graph showing the variation of intensity of polarized light transmitted by an analyzer.

Q.6> How does the (a) Pole strength and (b) Magnetic moment of each part of a bar magnet change if it is cut into two equal pieces transverse to its length

Q.7> An electron beam projected along + X-axis, experiences a force due to a magnetic field along the +Y-axis. What is the direction of the magnetic field?

Q.8> The electric field and electric potential at any point due to a point charge kept in air is 20 NC-1 and 10 JC-1 respectively. Compute the magnitude of this charge.

Q.9> Write the mathematical relation between mobility and drift velocity of charge carriers in a conductor. Name the mobile charge carriers responsible for conduction of electric current in (i) an electrolyte (ii) an ionized gas.

Q.10> Explain how the width of depletion layer in a p-n junction diode changes when the junction is (i) forward biased (ii) reverse biased.

Q.11> Why should the material used for making permanent magnets have high coercivity?

Q.12> Differentiate b/w AM and FM and explain why the latter is preferred.

Q.13> A convex lens of refractive index 1.5 has a focal length of 18 cm in air. Calculate the change in its focal length when it is immersed in a liquid having refractive index (a) 1.3 (b) 2

Q.14> Deduce an expression for the electric potential due to an electric dipole at any point on its axis. Mention one contrasting feature of electric potential of a dipole at a point as compared to that due to a single charge.

OR

A parallel plate capacitor, each with plate area A and separation d, is charged to a potential difference V. The battery used to charge it is then disconnected. A dielectric slab of thickness d and dielectric constant K is now placed between the plates. Explain what change, if any, will take place in

(i) charge on the plates (ii) electric field intensity between the plates (iii) capacitance of the capacitor.

Q.15> What is angle of dip? What is the angle of dip at (a) Poles (b) Equator

Q.16> What is meant by sensitivity of a potentiometer? A battery E of 4V and a variable resistance R are connected in series with the potentiometer wire AB ( length 1m ). When a cell of 1.5V is connected b/w AC no current flows through it. Length AC is 60cm.

(1) Find the potential difference b/w A and B

(2) Would the method work if battery E1 of 4V is replaced by a cell of 1V.

Q.17> Distinguish b/w diamagnetic and ferromagnetic substances in respect of their

(a) Intensity of magnetization

(b) Behavior in non uniform magnetic field.

(c) Susceptibility

Q.18> Draw a circuit diagram of a common emitter amplifier using npn transistor. Show input and output voltages graphically. The current gain is 59. If the emitter current is 6mA, find base and collector current.

Q.19> In a plot of photoelectric current versus anode potential, Justify, how does

(i) the saturation current vary with anode potential for different frequencies but same intensity ?

(ii) the stopping potential vary for incident radiations of different intensities but same frequency ?

(iii) photoelectric current vary for different intensities but same frequency of incident radiations ?

Q.20> A bar magnet, held horizontally, is set into angular oscillations in Earth magnetic field. It has time periods T1 and T2 at two places, where the angles of dip are θ1 and θ2 respectively. Deduce an expression for the ratio of the resultant magnetic fields at the two places.

Q.21> Verify Snell's law of refraction using Huygen's wave theory.

OR

Prove the law of reflection on the basis of wave theory.

Q.22> Derive an expression for the width of the central maximum for diffraction of light at a single slit. How does this width change with increase in width of the slit?

Q.23> Derive a mathematical expression for the force acting on a current carrying straight conductor kept in a magnetic field. State the rule used to determine the direction of this force.

Q.24> With the help of a labeled circuit diagram, explain how will you determine the internal resistance of a primary cell using a potentiometer. State the formula used.

Q.25> Derive an expression for the frequency of the side bands produced in Amplitude modulation. Under what condition can different stations operate without interfering?

Q.26> Show that the decay ratio 'R' of a sample of a radionuclide is related to the number of radioactive nuclei N at the same instant by the expression R = λN. Also Prove that the instantaneous rate of change of the activity of a radioactive substance is inversely proportional to the square of its half life.

Q.27> Two cells of EMF 1V, 2V and internal resistances 2 and 1 respectively are connected in
(i) series, (ii) parallel. What should be the external resistance in the circuit so that the current through the resistance be the same in the two cases? In which case more heat is generated in the cells?

Q.28> What is interference of light? Write two essential conditions for sustained interference pattern to be produced on the screen. Draw a graph showing the variation of intensity versus the position on the screen in Young’s experiment when (a) both the slits are opened and (b) one of the slits is closed.
What is the effect on the interference pattern in Young’s double slit experiment when:

(i) Screen is moved closer to the plane of slits?
(ii) Separation between two slits is increased. Explain your answer in each case.

OR

What is diffraction of light? Draw a graph showing the variation of intensity with angle in a single slit diffraction experiment. Write one feature which distinguishes the observed pattern from the double slit interference pattern.

How would the diffraction pattern of a single slit be affected when:

(i) The width of the slit is decreased?
(ii) The monochromatic source of light is replaced by a source of white light?

Q.29> State Biot-Savart’s law. Using this law, derive the expression for the magnetic field due to a current carrying circular loop of radius ‘R’, at a point which is at a distance ‘x’ from its centre along the axis of the loop. Show that this formula reduces to the formula for B at the centre of a coil in case of x = 0

(b) Two concentric coils have radius 4m and 5m. The smaller coil carries a current of 10A in the clockwise direction. What should be the magnitude and direction of current in the other so that the net magnetic induction at the common center is zero?

OR

Using a labeled diagram, explain the construction and working of a cyclotron. Mention 2 uses and briefly explain why a cyclotron can not accelerate an electron.

(b) A dees of a cyclotron have a radius Ro. Derive an expression for the maximum energy to which a charged particle q of mass m can be accelerated, Also prove that the cyclotron frequency is constant.

Q.30> Define capacitance of a capacitor. Give its unit. Derive an expression for the capacitance of a parallel plate capacitor in which a dielectric medium of dielectric constant K fills the space between the plates

OR

Explain the principle construction and working of a Van de graff generator.

(b) The radius of the metallic sphere is 10m and the dielectric strength of the gas is 108V/m. For safety reasons, the field should never exceed 20% of this value. What is the maximum charge that can be given to the sphere?

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