Question

Assertion : The temperature coefficient of resistance is always positive.
Reason : On increasing the temperature, the resistance of metals and alloys increase.
A) Both Assertion and Reason are true and Reason is the correct explanation of Assertion.
B) Both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
C) Assertion is true but Reason is false.
D) Assertion is incorrect but reason is correct.

Answer 1

Hint
When the temperature is increased, there are more effective collisions and hence more loss of energy occurs and if more energy is dissipated, will the resistance increase or decrease?

Complete step by step answer
When we talk about metals and we increase the temperature, the relative movement of the atoms and free electrons increase. Since the movement is more, hence due to this there are more collisions and more loss of energy due to which the resistance increases and it gives a positive temperature coefficient of resistance for metals due to the loss of energy.
So both Assertion and Reason are true and Reason is the correct explanation of Assertion.
Option (A) is correct.

Note
However, when we talk of semiconductors the charge carriers are electrons and holes. So the conductivity will depend upon electron-hole pairs which is given by the following formula,
$\Rightarrow E = {T^{\dfrac{3}{2}}}{e^{ - \dfrac{{{E_g}}}{{2{K_b}T}}}}$ where ${E_g}$= energy of band gap.
T is the temperature and ${K_b}$ is the Boltzmann constant.
As temperature increases the concentration of the electron-hole pairs increases which leads to an increase of conductivity and decrease in resistivity. So, a p-type semiconductor has a negative temperature coefficient of resistance.