Introduction to Electronics

Practice past-paper questions

Practise O/L exam questions on Introduction to Electronics with worked solutions

1. 2020 · Paper II · 5 marks
   A simple transistor switch circuit is used to turn a LED on and off. (i) Draw the symbol of an NPN transistor and label its three terminals. (ii) State the condition needed at the base terminal to allow current to flow from collector to emitter. (iii) Name ONE practical application of a transistor switch circuit.
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   (i) NPN transistor has three terminals: Base (B), Collector (C), Emitter (E). The arrow on the emitter points outward. (ii) A small forward-bias voltage (≥ 0.7 V for silicon) must be applied at the Base terminal to turn the transistor ON and allow current from Collector to Emitter. (iii) Automatic street lighting (light-dependent switch), alarm systems, or motor speed control.
   Source: NIE O/L Science 2020 Paper II Q12

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