JEE MAIN - Physics (2023 - 6th April Evening Shift - No. 7)
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 $$\mathrm{n}$$-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
Both A and R are correct but R is NOT the correct explanation of A
A is correct but R is not correct
A is not correct but R is correct
Both A and R are correct and R is the correct explanation of A
Explanation
A p-n junction consists of a p-type semiconductor (which has an excess of holes) in contact with an n-type semiconductor (which has an excess of electrons). In a forward-biased p-n junction, an external voltage is applied such that the positive terminal is connected to the p-side and the negative terminal is connected to the n-side. This configuration promotes the flow of majority charge carriers (holes from the p-side and electrons from the n-side) across the junction.
There are two types of currents in a p-n junction: drift current and diffusion current. Drift current is caused by the electric field due to the built-in potential, which opposes the flow of majority charge carriers. Diffusion current is caused by the concentration gradient of the charge carriers, which promotes the flow of majority charge carriers.
When the p-n junction is forward biased, the applied voltage reduces the potential barrier, allowing more majority charge carriers to flow across the junction. This results in an increase in the diffusion current. In a forward-biased p-n junction, the diffusion current is indeed greater than the drift current in magnitude, so Assertion A is correct.
Regarding Reason R: The diffusion current in a p-n junction is actually from the p-side to the n-side, as holes (majority charge carriers in the p-side) move from the p-side to the n-side, and electrons (majority charge carriers in the n-side) move from the n-side to the p-side. Therefore, Reason R is incorrect.
There are two types of currents in a p-n junction: drift current and diffusion current. Drift current is caused by the electric field due to the built-in potential, which opposes the flow of majority charge carriers. Diffusion current is caused by the concentration gradient of the charge carriers, which promotes the flow of majority charge carriers.
When the p-n junction is forward biased, the applied voltage reduces the potential barrier, allowing more majority charge carriers to flow across the junction. This results in an increase in the diffusion current. In a forward-biased p-n junction, the diffusion current is indeed greater than the drift current in magnitude, so Assertion A is correct.
Regarding Reason R: The diffusion current in a p-n junction is actually from the p-side to the n-side, as holes (majority charge carriers in the p-side) move from the p-side to the n-side, and electrons (majority charge carriers in the n-side) move from the n-side to the p-side. Therefore, Reason R is incorrect.
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