Reverse Biasing of a p-n Diode

When a p-n diode is reverse biased, the positive terminal of the battery is connected to the n-side of the diode, and the negative terminal is connected to the p-side. This creates an electric field that opposes the natural flow of current in the diode.

Understanding Resistance Measurement

To measure the resistance of a p-n diode using an ohm-meter, the diode is connected in parallel with the meter. The ohm-meter applies a small voltage across the diode and measures the resulting current flow. Based on Ohm's Law (V = IR), the resistance can be calculated by dividing the applied voltage by the measured current.

Resistance Measurement in Reverse Bias

When a p-n diode is reverse biased, the resistance measured by an ohm-meter connected across it will be high. This is because the electric field created by the reverse bias prevents the flow of current through the diode.

Explanation

1. Electric Field: When a p-n diode is reverse biased, the electric field created by the battery opposes the flow of majority charge carriers across the junction. This electric field widens the depletion region, which is the region near the junction where there are no majority charge carriers.

2. No Majority Charge Carriers: In the reverse biased condition, the depletion region becomes wider and acts as a barrier for majority charge carriers (electrons in the n-region and holes in the p-region) to cross the junction. As a result, very few charge carriers are available to conduct current through the diode.

3. Negligible Current Flow: Since the majority charge carriers are unable to cross the junction, the current flowing through the diode in reverse bias is negligible. Hence, the resistance measured by the ohm-meter connected across the diode is high.

4. Infinite Resistance vs. High Resistance: While the resistance measured is not truly infinite, it is considered high because the current flowing through the diode is very small compared to the applied voltage.

In summary, when a p-n diode is reverse biased, the electric field created widens the depletion region, preventing the flow of majority charge carriers and resulting in a high resistance measured by an ohm-meter connected across the diode.