Question

When a semiconductor is heated, its resistance
(A) Decreases
(B) Increases
(C) Remains unchanged
(D) Nothing is definite

Answer 1

Hint Semiconductors are materials whose resistance falls between the resistance of a conductor and an insulator. In the case of a conductor when the temperature increases the resistance increases because of the vibration of molecules. We see what happens in the case of a semiconductor to solve this question.

Complete Step by step solution When a material is heated the valence band and conduction band moves due to the energy from the heat. In the case of conductors, the valence band and conduction band overlap and resistance increase. In the case of semiconductors, the valence band conduction band has a gap before it is heated. When the semiconductor is heated the gap becomes small and resistance decreases because of the availability of electrons.

Hence when a semiconductor is heated its resistance decreases. Option (A) decreases is the correct answer.

Additional information Electrical resistance is the opposition offered to current flow in a circuit. It is measured in Ohms. Conductance is the opposite of resistance. The reciprocal value of resistance gives the value of conductance of a material.

Note We can also look at the explanation like, when the heat is transferred to a semiconductor, electrons start to vibrate creating more space for electrons to flow. In the case of conductors, there are excess electrons so the space decreases and the resistance increases. This is only for remembering purposes and not the exact explanation for the answer. Students might make a mistake by taking resistance as conductance if not read properly. Resistance and conductance are reciprocal of each other.