Question
In the given circuit diagram, a voltmeter ‘V’ is connected across a lamp ‘L’. How 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 a Common Emitter configuration of an npn transistor. Input circuit is forward biased and collector circuit is reverse biased.
i)
If the value of the resistance R is reduced, the current in the forward biased input circuit increases. The emitter current IE and the collector current IC (= IE – IB) both increase. Hence, the brightness of the lamp increases.
ii)
Due to increase in IC, the potential drop across lamp L increases and hence the voltmeter reading V increases.
