Q4. a) Explain the preference for a 60 Hz system. Describe the dangers of running a 50 Hz system from a 60 Hz supply. (6) b) A transistor amplifier stage comprises a transistor of parameters hie = 800 hfe = 5O and hoe = 20µ S, and bias components and coupling capacitors of negligible effect. The input signal consists of an e.m.f. of 60 mV from a source of internal resistance 2.2 k , and the total load on the stage output is 4 k . Determine the current, voltage and power gains of the amplifier stage. (10)
Q5. A) Explain how the efficiency and regulation of a transformer can be assessed by open circuit and short circuit tests? (6) b) A tuned circuit consisting of a coil having an inductance of 200 mH and a resistance of 20 Ω in parallel with a variable capacitor is connected in series with a resistor of 8000 Ω across a 60V supply having a frequency of 1 MHz Calculate: a) The value of C to give resonance. b) The dynamic impedance and the Q factor of the tuned circuit. c) The current in each branch. (10)
Q6. a) Explain distribution factor and pitch factor for alternator windings. (6) b) An eight-pole armature is wound with 480 conductors. The magnetic flux and the speed are such that the average e.m.f. generated in each conductor is 2.2 V, and each conductor is capable of carrying a full load current of 100 A. Calculate the terminal voltage on no load, the output current on full load and the total power generated on full load when the armature is a) lap-connected b) wave-connected (10)
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