What does resistance measure?

Resistance measures the opposition to the flow of electric current in a circuit. It quantifies how much a material resists the movement of electrons, which is essential for understanding how electrical circuits function. Higher resistance means that less current will flow for a given voltage, according to Ohm's Law (V = IR), where V is voltage, I is current, and R is resistance. This concept is fundamental in both theoretical and practical aspects of electrical engineering and is critical for designing circuits and understanding their behavior under different conditions.

The other options relate to different electrical properties but do not accurately reflect what resistance itself measures. The voltage drop across a circuit is influenced by the resistance but does not define it. Current flow is a result of voltage and resistance rather than a measure of resistance itself. Energy lost as heat involves resistance in a sense (Joule heating), but it is not a direct measure of how much resistance exists in a circuit. Understanding resistance is vital for predicting how changes in voltage or circuit components will affect overall performance.