What type of circuit reading requires power to be applied?

The correct choice, which pertains to voltage, involves understanding the concept of circuits and electrical measurements. Voltage readings require power to be applied because voltage is essentially the electrical potential difference between two points in a circuit. Without power, there is no potential difference to measure, which means no voltage can be detected.

When you measure voltage, you're usually using a voltmeter, which is connected across two points in a live circuit. If the circuit is not powered, the voltmeter will register zero because there is no electrical potential driving the flow of electricity between those points.

In contrast, resistance can be measured in an unpowered circuit, as it is the opposition to current flow and can often be assessed using an ohmmeter when power is disconnected. Current measurement similarly does not require voltage to be applied but involves assessing the flow of electrons when the circuit is active. The option related to Ohm's law reflects the relationship between voltage, current, and resistance, but it does not specifically indicate the need for power to be applied. Only voltage measurements inherently require an active circuit to provide meaningful readings.