Question

Assertion: The temperature coefficient of resistance is positive for metals and negative for p-type semiconductors.
Reason: The effective charge carriers in metals are negatively charged whereas in p-type semiconductors they are positively charged.

• A. If both Assertion and Reason are true and the Reason is a correct explanation of the Assertion
• B. If both Assertion and Reason are true but Reason is not a correct explanation of the Assertion
• C. If Assertion is true but the Reason is false
• D. If both Assertion and Reason are false

Answer 1

Answer: (B)

In case of metals when we increase the temperature, the relative movement of the atoms as well the free clectrons increase. Becasue of which there is more collisions and more loss of energy. Due to which the resistance increases and it gives a positive temperature coefficient of resistance for metals.
But in the case of a semiconductor $(p$ -type or $n$ -type) the charge carriers are electrons and holes. So the conductivity will depend upon the number of such electron-hole pairs. At any time this number of electron-hole pairs is proportional to $T^{3 / 2} e^{-\Delta E / 2 K T}$, where $\Delta E$ is the band gap. Now with increase of temperature, the concentration of the electron-hole pairs increases which leads to an increase of conductivity or conversely a decrease of resistivity. So, a $p$ -type semiconductor has a negative temperature coefficient of resistance.