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.

Answer 1

The given figure is Common Emitter(CE) configuration of an npn transitor is shown in the figure. The input circuit is forward biased and a collector circuit is reverse biased.
If resistance R decrease forward biased in the input circuit will increase, thus the base current $I_0$ will decrease and the emitter current $I_E$ will increase. This will increase the collector current $I_C$ as $I_E=I_C+I_B$
When $I_C$ increase which flows through the lamp, the voltage across the bulb will also increase making the lamp brighter and the voltmeter is connected in parallel with the lamp, the reading in the voltmeter will also increase.