Final answer:
An ohmmeter is used to test a switch that is removed or isolated from the circuit. It operates based on Ohm's law, measuring resistance to assess the switch's functionality without requiring connection to a live circuit.
Step-by-step explanation:
When testing a switch that has been removed or isolated from the circuit, an ohmmeter is the appropriate testing device to use. An ohmmeter is designed to measure resistance without requiring a live circuit, ensuring safety and accuracy. The instrument operates on the principle of Ohm's law and typically uses an internal voltage source to pass current through the switch. By measuring the resulting current flow, the ohmmeter calculates the resistance, indicating whether the switch is functioning correctly (typically showing low or no resistance when closed, and infinite resistance when open).
It is crucial to isolate the component when using an ohmmeter because connecting it to a live circuit can damage the meter. When the ohmmeter is used correctly, it will indicate whether the switch maintains continuity (closed circuit) or not (open circuit), thus confirming its operational state.