Which unit measures electrical resistance?

• A. Ampere (A)
• B. Ohm (Ω)
• C. Volt (V)
• D. Watt (W)

Answer: (B)

Resistance is measured in ohms (Ω). This comes from Ohm’s law, which shows resistance as R = V / I. That means the unit for resistance is volts per ampere, and by definition that combination is the ohm. So if 1 volt of potential difference drives 1 ampere of current through a conductor, the resistance is 1 ohm.

To place it in context with the other common units: ampere measures current—the amount of charge flowing per second. volt measures the electric potential difference that pushes the current. watt measures power, the rate at which work is done or energy is transferred, and equals volts times amperes. One ohm is specifically the ratio of voltage to current, hence its role as the unit of resistance.