Recreational Vehicle (RV) Technician Practice Test

When testing a good diode with an ohmmeter, what readings should you expect when the leads are reversed?

1. Two low readings

2. One low reading and one high (infinite) reading

3. Two high readings

4. One high (infinite) reading and one low reading

The correct answer is: One low reading and one high (infinite) reading

When testing a good diode with an ohmmeter, reversing the leads will demonstrate its rectifying behavior. A silicon diode, for instance, allows current to flow in one direction (forward bias) and blocks it in the opposite direction (reverse bias). In forward bias, connecting the positive lead of the ohmmeter to the anode and the negative lead to the cathode, a low resistance reading indicates that the diode is functioning correctly. This confirms that it allows current to pass through as intended. On the other hand, when the leads are reversed, the positive lead connects to the cathode and the negative lead to the anode, which places the diode in reverse bias. In this configuration, a good diode should block current flow, resulting in a high (or infinite) resistance reading. Thus, expecting one low reading (in forward bias) and one high reading (in reverse bias) when testing with an ohmmeter accurately reflects the dual behavior of a diode, confirming its proper function.