Which of the following is correct?

Question

Question

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KVS TGT WET (Work Experience Teacher) Official Paper

Conductors and extrinsic semiconductors have negative temperature coefficient and intrinsic semiconductors have positive temperature coefficient.
Insulators and semiconductors have positive temperature coefficient whereas conductors have negative temperature coefficient.
Conductors and extrinsic semiconductors have positive temperature coefficient and pure semiconductors have negative temperature coefficient.
Intrinsic and extrinsic semiconductors have negative temperature coefficient and conductors have positive temperature coefficient.

Answer 1

Concept:

Temperature coefficient of resistance (α) :

The change in electrical resistance of a substance with respect to a per degree change in temperature.
α depends on the type of material.

Variation of resistance with temperature:

Let R0 and RT represent the resistance at a temperature of T0 and T respectively. Therefore

RT = R0 [1+ α (T-T0)]

Where α is the temperature coefficient of resistance.

Explanation:

α for conductors:

In metal, if the temperature increases, the resistance of the metal increases with the rise in temperature.
So, we consider the temperature coefficient of resistance as positive for metal.

α for semiconductor:

If temperature increases, the number of electrons come to the conduction bands from valence bands by crossing the forbidden energy gap.
As the number of free electrons increases, the resistance of this type of non-metallic substance decreases with an increase in temperature.

Hence, the temperature coefficient of resistance is negative for non-metallic substances and semiconductors.

Both Intrinsic & Extrinsic Semiconductors will have negative temperature coefficient. Conductors have positive temperature coefficient.