Physics Sample Paper Class XII
Set - 3

 1. Draw an equipotential surface in a uniform electric field. (1 mark)

 2. If a wire is stretched to double its original length without less of mass, how will the resistivity of the wire be influenced? (1 mark)

 3. Why do magnetic lines of force prefer to pass through iron than through air? (1 mark)

 4. What is the power factor of an LCR series circuit at resonance? (1 mark)

 5. Why is the transmission of signals using ground waves restricted to frequencies upto 1500 kHz? (1 mark)

 6. The polarising angle of a medium is 60^o. What is the refractive index of the medium? (1 mark)

 7. How does the collector current change in a junction transistor, if the base region has larger width? (1 mark)

 8.Two stars A and B have magnitudes -2 and +4 respectively. Which star appears brighter? (1 mark)

 9. An electric flux of -6 x 103 Nm2/C passes normally through a spherical Gaussian surface of radius 10 cm, due to a point charge placed at the center.

(i) What is the charge enclosed by the Gaussian surface?

(ii) If the radius of the Gaussian surface is doubled, how much flux would pass through the surface? (2 marks)

 10. Three identical resistors, each of resistance R, when connected in series with a d.c. source, dissipate power X. If the resistors are connected in parallel to the same d.c. source, how much power will be dissipated? (2 marks)

 11. Define mutual inductance. State two factors on which the mutual inductance between a given pair of coils depends. (2 marks)

 12. Light from a galaxy, having wavelength of 6000 Ao, is found to be shifted towards red by 50 Ao. Calculate the velocity of recession of the galaxy. (2 marks)

 13. A converging lens has a focal length of 20 cm in air. It is made of a material of refractive index 1.6. If it is immersed in a liquid index 1.3, what will be its new focal length? (2 marks)

 14. Draw a labelled ray diagram to show the image formation in astronomical telescope for normal adjustment position. Write down the equation for its magnifying power. (2 marks)

 15. The half-life of a radioactive sample is 30 seconds. Calculates (i) the decay constant, and (ii) time taken for the sample to decay to 3/4th of its initial value. (2 marks)

 16. Draw a logic circuit diagram showing how a NAND gate can be converted into a NOT gate. (2 marks)

 17. What is an ideal diode? Draw the output waveform across R, for the input waveform given below : (2 marks)

 18. Write, in brief, the method to determine the distance of an inferior planet from the sun. (2 marks)

 19. Explain, with the help of a circuit diagram, the use of potentiometer for determination of internal resistance of a primary cell. Derive the necessary mathematical expression. (3 marks)

 20. Calculate the resistance between A and B of the given network. (3 marks)

 21. State Faraday's laws of electrolysis. Write down the relation connecting chemical equivalent and electro-chemical equivalent. (3 marks)

 22. An electron is moving at 106m/s in a direction parallel to a current of 5 A, flowing through an infinitely long straight wire, separated by a perpendicular distance of 10 cm in air. Calculate the magnitude of the force experienced by the electrons. (3 marks)

 23. A bar magnet, held horizontally, is set into angular oscillations in Earth's magnetic field. It has time periods T1 and T2 at two place, where the angles of dip are α₁ and α₂ respectively. Deduce an expression for the ratio of the resulting magnetic field at the two places. (3 marks)

 24. Verify Snell's law of refraction using Huygens' wave theory. (3 marks)

 25. Find the position of an object which when placed in front of a concave mirror or focal length 20 cm, produces a virtual image, which is twice the size of the object. (3 marks)

 26. If the frequency of the incident radiation on the cathode of a photo cell is doubled, how will the following change:

(i) Kinetic energy of the electrons,

(ii) Photoelectric current,

(iii) Stopping potential.

Justify you answer. (3 marks)

 27. Explain, with the help of a circuit diagram, why the output voltage is out of phase with the input voltage in a common emitter transistor amplifier. (3 marks)

 28. With the help of a labelled diagram, describe Millikan's oil-drop experiment for determining the charge of an electron. (5 marks)

 29. Draw the curves showing the variation of inductive reactance and capacitive reactance with applied frequency of an a.c source. A capacitor, a resistor of 5 ohm, and an inductor of 50 mH are in series with an a.c. source marked 100 V, 50 Hz. It is found that voltage is in phase with the current. Calculate the capacitance of the capacitor and the impedance of the circuit. (2+3 marks)

 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 Graaff generator. (5 marks)