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Question
In the following diagram 'S' is a semiconductor. Would you increase or decrease the value of R to keep the reading of the ammeter A constant when S is heated? Give reason for your answer.
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Solution
As the semiconductors at room temperature act as insulators so they offer very high resistance value. But with the increase in temperature, they start conducting by decreasing the energy-gap and hence they offer less resistivity. So, the resistivity of semiconductors decreases with the increase in temperature and as a result resistance also decreases.
So to maintain the constant reading on the ammeter, we should increase the value of variable resistance R to compensate with the decreased value of resistance for semiconductor.
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