Question

In a semiconductor, the conductivity increases with increase in temperature because

• A. Resistance increases
• B. Number of free charge carriers increases
• C. Mobility becomes zero
• D. Band gap increases

Hint:

For semiconductors: \[ \boxed{\text{Temperature} \uparrow \Rightarrow \text{Conductivity} \uparrow} \] This is opposite to metals where: \[ \boxed{\text{Temperature} \uparrow \Rightarrow \text{Resistance} \uparrow} \] CUET frequently asks this comparison.

Answer 1

The Correct Option is B

Step 1: Recall the behavior of semiconductors. Semiconductors have a small energy band gap. At room temperature, only a limited number of electrons are available for conduction.

Step 2: Understand the effect of temperature. When temperature increases, more electrons gain sufficient energy to jump from the valence band to the conduction band. Thus: \[ \text{Number of electrons} \uparrow \] \[ \text{Number of holes} \uparrow \]

Step 3: Determine the effect on conductivity. Since conductivity depends on the number of charge carriers, \[ \sigma \propto n \] an increase in charge carriers increases conductivity. Therefore, \[ \boxed{\text{Number of free charge carriers increases}} \] Hence, the correct answer is: \[ \boxed{\text{(B)}} \]