Can resistance be measured with power applied?

Resistance can only be accurately measured when there is no power applied to the circuit. This is because applying power can introduce other factors, like voltages and currents that could affect the reading. When power is applied, the components in the circuit might behave differently due to their operational characteristics, such as heating effects, which can lead to changes in resistance.

In contrast, measuring resistance with power off ensures that the component is at a stable state, allowing the multimeter to send a small test current through the component without interference from additional voltages, thus providing an accurate resistance value.

For instance, if you tried to measure the resistance of a resistor while power is flowing through it, the reading you obtain would not reflect the true resistance due to the influence of the active circuit conditions, which could include varying levels of current or components in different operational states. Therefore, measuring resistance requires the circuit to be de-energized to guarantee a consistent and accurate result.