What can indicate the presence of voltage in a circuit?

The presence of voltage in a circuit can be effectively indicated by a glowing LED indicator. LEDs, or light-emitting diodes, require a certain voltage to illuminate. When an adequate voltage is applied across the LED, it allows current to flow, causing the LED to emit light. This visible indication serves as a straightforward and immediate way to determine that voltage is present in the circuit.

In contrast, while disconnected capacitors or multimeters set to measure resistance can provide information about the circuit, they do not directly indicate the presence of voltage. A disconnected capacitor will not show any voltage since it is not connected to the circuit, and a multimeter set to measure resistance typically checks for continuity and resistance values rather than voltage. A thermal imaging camera detects heat rather than electrical voltage, which makes it unsuitable for directly indicating voltage presence in a circuit.