Diodes, Transistors and Simple Circuits — O/L Science

How do I practise Diodes, Transistors and Simple Circuits?

1 question with a worked solution · 5 marks

1. 2020 · Paper II · 5 marks
   Question 12 sets a simple transistor switch circuit driving an LED. It asks you to draw the NPN transistor symbol with its three terminals labelled, to state the condition needed at the base for current to flow from collector to emitter, and to name one practical application of such a switch.
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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: Department of Examinations, Sri Lanka — G.C.E. O/L Science 2020, Paper II, Question 12 · https://doenets.lk/pastpapers

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