148. A single phase ac regulator fed from 50 Hz system supplies a load having resistance and inductance of 4.0 ohms and 12.73 mH respectively. The control range of firing angle is
A. 0?< a < 180?
B. 45? < a < 180?
D. 0?< a <45?
149. It is required to drive a dc shunt motor at different speeds in both the directions (forward and reverse) and also to brake it in both the directions. Which one of the following would you use?
A. a half-controlled thyristor bridge
B. a full-controlled thyristor bridge
C. a dual converter
D. a diode bridge
150. The frequency of ripple in the output voltage of a three-phase half controlled bridge rectifier depends on the
A. firing angle
B. lead inductance
C. load resistance
D. supply frequency
151. A fully controlled 3-phase converter has to supply an output voltage of 270 volts. The minimum secondary line voltage of the input transformer is volts.
D. none of these
152. In the circuit shown in Fig. 8.8 the resistance R is varied from 0 to co.
A. The phase remains constant.
B. The phase varies from 0 to ? 90?
C. The magnitude is constant and phase varies from 0 to 180?
D. The phase of the circuit is given by 1 2 tan-I coCR
153. The interbase resistance of a UJT is
A. less than forward biased pn diode
B. higher than a FET
C. of the order of 1 K and less
D. in the range of 5 K to 10K
154. VI characteristic of emitter of a UJT is
A. similar to CE with linear and saturation region.
B.similar to FET with a linear and pinch off region.
C. similar to tunnel diods in some respects.
D. linear between the peak point and valley point.
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