Q4. (a) Why is a synchronous motor not self-starting? What are the various ways in which it can be started?
(b) Differentiate Ge and Si diode characteristics. The reverse bias saturation current for a P-N junction diode is 1.0 µA at 300 K. Determine its AC resistance at 150 mV Forward bias. (10)
Q5. a) Describe the no-load saturation characteristics of a D.C. generator. (6)
b) A coil of inductance 2 H and unknown resistance is connected to a D.C. supply of 100 volts. After 4 ms the current has risen to 75% of its final steady state value. Calculate EACH of the following:
(a) The resistance by the coil. (6)
(b) The energy stored in the coil when the current has reached its steady state value. (6)
Q6. a) What is back emf? Derive the relation for the back emf and the supplied voltage in terms of armature reactance. (6)
b) Two earth lamps at 120 V, 15 W are used on a 110 V distribution circuit. Due to damage to a motor, the resistance of the positive line is reduced to 10 ohm and that of the negative line to 5 ohm. Find the voltage across each lamp and the extra load on the generator due to the fault. (10)
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