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Question
In the given circuit diagram a voltmeter ‘V’ is connected across a lamp ‘L’. Ho would (i) the brightness of the lamp and (ii) voltmeter reading ‘V’ be affected, if the value of resistance ‘R’ is decreased? Justify your answer.
Solution
The given figure is Common Emitter (CE) configuration of an npn transistor. The input circuit is forward biased and collector circuit is reverse biased.
As the base resistance R decreases, the input circuit will become more forward biased thus decreasing the base current (IB) and increasing the emitter current (IE). This will increase the collector current (IC) as IE = IB + IC.
When IC increases which flows through the lamp, the voltage across the bulb will also increase thus making the lamp brighter and as the voltmeter is connected in parallel with the lamp, the reading in the voltmeter will also increase.
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