A battery and a test light can be used to:

• A. Test continuity of a circuit.
• B. Calculate the resistance of a circuit.
• C. Test how much inductance is in a circuit.
• D. Prevent a system from losing power.

Answer: (A)

Continuity testing is what you’re doing when you use a battery and a test light. If there’s a complete path from the battery through the wiring to the load, current can flow and the test light will glow. If the path is broken anywhere—open circuit, loose connection, or a blown fuse—the current can’t flow and the light stays off. This lets you quickly confirm whether a circuit is complete and capable of carrying current, which is exactly what continuity checks look for in practice.

Trying to calculate the resistance of a circuit requires precise measurements of current and voltage (or using an ohmmeter), not a simple DC lamp. Testing for inductance needs AC signals and specialized equipment like an LCR meter. And preventing a system from losing power isn’t accomplished by this test setup—it’s a function of power management or backup systems, not continuity testing.