56. The mid frequency gain of an R-C coupled common emitter transistor amplifier is 100. The lower and upper cutoff frequencies of amplifier are 20 Hz and 20 kHz respectively. Find the frequency in lower frequency region where voltage gain is 60. (1) 7.5 Hz (2) 15 Hz (3) 18 Hz (4) 26.66 Hz 57. The condition for sustained oscillations is phase shift oscillator is (he-forward current gain ratio) (2) he <56 (1) he56 (3) he28 (4) he >0 58. The order of input impedance of FET is (1) 0.12 to 12 (2) 10 2 to 1000 2 (3) 1000 2 to 10000 2 (4) 1 to several hundred 59. If air film is formed in Newton's Ring experiment, then ratio of diameter of first four bright rings are 60. (1) 1:2:3:4 (2) 4 (3) 1:3:5:7 (4) 1:3:5:7 Which statement is false about LASER ? (1) In the absence of resonator cavity, there would be no amplification of light. (2) In laser the active medium is the amplifying medium. (3) Laser is a light source and analogous to an electronic oscillator. (4) In laser the rate of spontaneous emission is higher than stimulated (induced) emission.