CBSE Guess > Papers > Important Questions > Class XII > 2013 > Physics > Physics - by Mr. Raghu Sharma

CBSE CLASS XII

Physics

41. An alternating voltage of frequency f is applied across a series LCR circuit. Let fr be the resonance frequency for the circuit. Will the current in the circuit lag, lead or remain in phase with the applied voltage when
    1. 
    2. Explain your answer in each case.
42. Define 'electric line of force' and give its two important properties.
43. Define the terms 'Magnetic Dip' and 'Magnetic Declination' with the help of relevant diagrams.
44. Find the wavelength of electromagnetic waves of frequency 5 x 1019Hz in free space. Give its two applications.
45. What is an 'analog signal' and a 'digital signal'? How can an analog signal be converted into & digital signal?
46. A T.V. tower has a height of 400 m at a given place. Calculate as coverage range, if the radius of the earth is 6400 km.
47. With the help of a diagram, show the biasing of a light emitting diode (LED). Give its two advantages over conventional incandescent lamps.
48. An a.c. voltage of 100 V, 50 Hz is connected across a 20 ohm resistor and  2mH inductor in series. Calculate
    1. impedance of the circuit,
    2. rms current in the circuit.
49. A galvanometer has a resistance of It gives full scale deflection with a current of 2 mA. Calculate the value of the resistance needed to convert it into an ammeter of range 0-0.3 A.
50. The output of an OR gate is connected to both the inputs of a NAND gate. Draw the logic circuit of this combination of getes and write its truth table.
51. Two point charges and are separated by a distance of 1 m in air. Calculate at what point on the line joining the two charges is the electric potential zero.
52. The output of a 2-input NOR gate is fed to a NOT gate. Draw the logic circuit of this combination of gates and write the truth table for the output of the combination for all inputs.
53. Write any four characteristics of electromagnetic waves. Give two uses each of
    1. Radio-waves
    2. Micro-waves
54. Explain with the help of a labelled diagram the underlying principle and working of a step-up transformer. Why cannot such a device be used to step-up d.c. voltage ?
55. State the laws of radioactive decay. Establish a mathematical relation between half-life period and disintegration constant of a radioactive nucleus.
56. How is the mutual inductance of a pair of coils affected when
    1. separation between the coils is increased?
    2. the number of turns of each coil is increased ?
    3. a thin iron sheet is placed between the two coils, other factors remaining the same?
    Explain your answer in each case.
57. Define the terms threshold frequency and stopping potential in relation to the phenomenon of photoelectric effect. How is the photoelectric current affected on increasing the
    1. frequency
    2. intensity of the incident radiations and why?
58. State Gauss' theorem. Apply this theorem to obtain the expression for the electric field intensity at a point due to an infinitely long, thin, uniformly charged straight wire and at any point outside a uniformly charged thin spherical shell.
59. Explain
    1. forward biasing,
    2. reverse biasing of a P-N junction diode. With the help of a circuit diagram, explain the use of this device as a half - wave rectifier.
60. 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.

Submitted By : Mr. Raghu Sharma
Email: [email protected]