Question

In a P-N junction, there is no appreciable current if (A) a potential difference is applied across the junction (B) it is impossible (C) P-section is a made positive and N-section negative (D) a potential difference is applied across junction making P section negative and N-section positive.

Short answer

In a P-N junction, there is no appreciable current when a potential difference is applied across the junction, making the P-section negative and the N-section positive. This condition is known as reverse bias, where the applied voltage increases the barrier created by the depletion region, preventing the current flow. Therefore, the correct answer is (D).

Step-by-step solution

Understanding the P-N junction

In a P-N junction, the p-section (p-type material) has an excess of positively charged holes, while the n-section (n-type material) has an excess of negatively charged electrons. When the junction is formed, the electrons from the n-section recombine with the holes in the p-section, creating a depletion region near the junction with no charge carriers. The electric field from this region opposes the further movement of electrons and holes across the junction.

Analyzing Option (A)

Option (A) states that there is no appreciable current if a potential difference is applied across the junction. However, this statement is too general. The direction and magnitude of the applied potential difference, or voltage, determine the behavior of the P-N junction, as we will see in the other options.

Analyzing Option (B)

Option (B) claims that having no appreciable current in a P-N junction is impossible. This statement is incorrect because there are specific conditions under which the P-N junction will not have an appreciable current, as we will discuss in the following options.

Analyzing Option (C)

Option (C) suggests that having no appreciable current occurs when the P-section is made positive and the N-section negative. This condition is known as forward bias because the applied voltage helps to overcome the barrier created by the depletion region and allows the current to flow. When the P-N junction is forward-biased, the electrons from the n-side can move to the p-side and recombine with holes, creating a current flow. Thus, option (C) is incorrect.

Analyzing Option (D)

Option (D) states that having no appreciable current occurs when a potential difference is applied across the junction, making the P-section negative and the N-section positive. This condition is known as reverse bias because the applied voltage increases the barrier created by the depletion region, preventing the current flow. When the P-N junction is reverse-biased, the electrons in the n-side and the holes in the p-side are both moved away from the junction, and the depletion region widens. Consequently, there is no appreciable current in the P-N junction under this condition. Solution: Based on our analysis, the correct answer is (D) a potential difference is applied across the junction, making the P-section negative and the N-section positive.