ETO ETO Exam papers 📅 Aug 2023

Exam Question

(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 = 800Ω hfe = 50 and hoe = 20µS, 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 kΩ, and the total load on the stage output is 4 kΩ. Determine the current, voltage and power gains of the amplifier stage. (10)

Reference Answer

(a) Preference for a 60Hz system:
Higher frequency allows for the use of smaller and less expensive transformers for the same power handling capacity.
The higher frequency minimises the noticeable flicker often associated with incandescent lamps operating on lower frequencies.
Harmonics, unwanted frequencies that can interfere with the power supply, are easier to filter out with a 60 Hz system.

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