CBSE Guess > Papers > Important Questions > Class XII > 2013 > Physics > index > Physics - by Mr. Ajay Yadav

CBSE CLASS XII

Physics

1. How is the relative permeability (µr) of a material related to its susceptibility (χm) ?
2. A metallic wire 1 m in length is moving normally across a field of 0.1 T with a speed of 5 ms-1. Find the emf between the ends of the wire.
3. For which frequency of light, the human eye is most sensitive ?
4. If a plane glass slab is placed on letters of different colours, then red coloured letters appear more raised up. Why ?
5. If the maximum kinetic energy of electrons emitted in a photo-cell is 5 eV, what is the stopping potential ?
6. Is the ionization energy of an isolated free atom different from the ionization energy for the atoms in a crystalline lattice ?.
7. What is the de Broglie wavelength (A0 ) associated with an electron accelerated through a potential of 100 V ?
   
8. Two plane sheets of charge densities +σ and – σ are kept in air as shown in Fig. what are the electric field intensities at points A and B ?
   
9. What is the magnitude of magnetic force per unit length on a wire carrying a current of 8 A and making an angle of 300 with the direction of a uniform magnetic field of 0.15 T ?
10. State Lenz’s law. Predict the polarity of the capacitor in the situation described by fig.
    
11. (i) Draw the graphs showing variation of inductive reactance and capacitive reactance with frequency of applied a.c. source.
    (ii) Can the voltage drop across the inductor or the capacitor in a series LCR-circuit be greater than the applied voltage of the a.c. source ? Justify your answer.
12. (i) Draw a circuit diagram of a common emitter amplifier using n-p-n transistor. Show input and output voltages graphically.
13. (i) Give any one difference between FAX and Email systems of communication.
    (ii) A carrier wave of peak voltage 12 V is used to transmit a message signal. What should be the peak voltage of the modulating signal in order to have a modulation index of 75% ?
14. Name the following constituent radiations of electromagnetic spectrum which :
    (i) produce intense heating effect.
    (ii) is absorbed by the ozone layer in the atmosphere.
    (iii) is used for studying crystal structure.
15. State Gauss theorem and draw a graph between electric field due to an infinite plane charged sheet and distance.
16. An infinite line charge produces a field of 9 x 104 NC-1 at a distance of 2 cm. Calculate the linear charge density.
17. Define the term current density of a metallic conductor. Deduce the relation connecting  2 current density (J) and conductivity (σ) of the conductor, when an electric field E is applied to it.
18. Explain why does a convex lens behave as a converging lens when immersed in water (µ=1.33) and as a diverging lens, when immersed in carbon disulphide (µ=1.6).
19. State the principle of metre bridge. With the help of circuit diagram, explain how will you find out an unknown resistance ?
20. (i) State the principle of transformer.
    (ii) Show that in the free oscillations of an LC circuit, the sum of energies stored in capacitor and the inductor is constant in time.
    

    OR

    1. In India, domestic power supply is at 220 V, 50 Hz, while in USA it is 110 V, 50 Hz. Give one advantage and one disadvantage of 220 V supply over 110 V supply.
    2. In an a.c. circuit, R=4Ω , Z=5 Ω, Vrms=200 V and Irms =1.5 A. Calculate the average power consumed over a full cycle.

Submitted By : Mr. Ajay Yadav
Email: [email protected]