Question

A good diode checked by a multimeter should indicate:

• A. high resistance in reverse bias and a low resistance in forward bias
• B. high resistance in both forward bias and reverse bias
• C. low resistance in both reverse bias and forward bias
• D. high resistance in forward bias and low resistance in reverse bias

Hint:

Quick diode test rule: Forward bias → low resistance Reverse bias → high resistance If both sides show low resistance, diode is faulty.

Answer 1

The Correct Option is A

To check a diode's functionality using a multimeter, it's essential to understand how diodes behave in different bias conditions:

1. In forward bias (positive voltage on the anode relative to the cathode), a good diode allows current to flow easily. Hence, it should indicate low resistance.
2. In reverse bias (positive voltage on the cathode relative to the anode), a good diode blocks current flow. Thus, it should indicate high resistance.

Therefore, when checking a good diode with a multimeter:

• Forward Bias: Connect the positive lead to the anode and the negative lead to the cathode. The resistance reading should be low.
• Reverse Bias: Connect the positive lead to the cathode and the negative lead to the anode. The resistance reading should be high.

Based on this understanding, the correct answer is: high resistance in reverse bias and a low resistance in forward bias.

The other options can be ruled out as follows:

• High resistance in both forward bias and reverse bias: This would indicate that the diode is not conducting properly in forward bias.
• Low resistance in both reverse bias and forward bias: This scenario suggests that the diode has failed and is allowing current in both directions, indicating a shorted diode.
• High resistance in forward bias and low resistance in reverse bias: This configuration is incorrect for a typical diode, as it should conduct in forward bias and block in reverse.

Answer 2

A quick way to think about this is from the multimeter user's point of view: what should the reading show as you flip the probes across a healthy diode?

When the red (positive) probe touches the diode's anode and the black (negative) probe touches its cathode, the diode is forward biased, current is allowed to flow, so a good diode lets a substantial current pass and the meter displays a low resistance.

When the probes are swapped, red on the cathode and black on the anode, the diode is now reverse biased, and a healthy junction should block almost all current except a negligible leakage, so the meter displays a high resistance, often reading as open-circuit on many meters.

If a diode instead showed the same reading in both directions, that would signal a fault: a low reading both ways means the junction has failed short, and a high reading both ways means it has failed open. A functioning diode must show a clear contrast between the two directions, low resistance one way, high resistance the other.

The pattern that fits a genuinely working diode is therefore: high resistance when reverse biased, and low resistance when forward biased.

Therefore, the correct answer is high resistance in reverse bias and a low resistance in forward bias.