Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R
Assertion A: Diffusion current in a p-n junction is greater than the drift current in magnitude if the junction is forward biased.
Reason R: Diffusion current in a p-n junction is from the n-side to the p-side if the junction is forward biased.
In the light of the above statements, choose the most appropriate answer from the options given below

Solution

Physics sir · 4 steps

In forward bias diffusion wins easily, but its current flows from p to n, not n to p.

1. Two currents. A p-n junction always carries two currents. Diffusion current comes from majority carriers crossing the junction, and drift current comes from minority carriers swept across by the junction field.
2. Check Assertion A. Forward bias lowers the potential barrier, so a large number of majority carriers can now diffuse across. Drift current depends only on the few minority carriers, so it stays tiny. Diffusion current is therefore much larger than drift current, and A is correct.
3. Check Reason R. Holes diffuse from the p-side to the n-side, and electrons diffuse from the n-side to the p-side. Electrons moving from n to p carry conventional current from p to n, so both flows give a diffusion current from the p-side to the n-side. R gives the opposite direction, so R is wrong.
4. So. A is correct but R is not, which is option (b).

The idea to keep. Current direction is the direction holes move, or opposite to electron motion. In forward bias both carriers diffuse in a way that sends current from p to n, the same way the external current flows.

Answer from the NTA final answer key. Solution by PrepWiser.