218. A zener diode works on the principle of
A. tunnelling of charge carriers across the junction
B. thermionic emission
C. diffusion of charge carriers across the junction
D. hoping of charge carriers across the junction

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219. When a line commutated converter operates in the inverter mode
A. it draws both real andreactive power from the A.C. supply
B. it delivers both real and reactive power to the A.C. supply
C. it delivers both real and reactive power to the A.C. supply
D. it draws reactive power from the A.C. supply

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220. The speed and torque of induction motors can be varied by which of the following means : 1. Stator voltage control 2. Rotor voltage control 3. Frequency control
A. 1 only
B. 2 only
C. 1 and 2 only
D. 1,2 and 3

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221. Staticinduction thyristors have
A. high dv / dt and low di / dt
B. low dv / dt and high di / dt
C. low dv / dt and low di / dt
D. high dv / dt and high di / dt

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222. MOS controlled thyristors have 1. Low forward voltag drop during conduction 2. Fast turn-on and turn-off time 3. Low switching losses 4. High reverse voltage blocking capability 5. Low gate input impedance of these statements
A. 1,2 and 3 are correct
B. 3,4 and 5 are correct
C. 2,3 and 4 are correct
D. 1, 3 and 5 are correct

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223. For a sinusoidal input voltage Vs = Vm sin cot = J5.T Vs sin cot If the input voltage is connected to load for n cycles and is disconnected for m cycles, the rms output voltage is given by Vo = Vs IF( where duty cycle K is given by
A.m+n
B. m ? n
C. mn
D. n/(m + n)

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224. A SCHOTTICY diode is a
A. majority carrier device
B. minority carrier device
C. fast recovery diode
D. both a majority and a minority carrier diode

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