In the formula I = E/R, what does E represent?

• A. resistance
• B. current
• C. voltage
• D. energy

Answer: (C)

In Ohm’s law, current is found by dividing the driving potential by the resistance. The symbol E represents the voltage, or electromotive force, supplied by the circuit. It’s the potential difference that pushes charges to move, measured in volts. Since voltage is energy per unit charge, it’s the correct quantity to use here rather than total energy.

For example, with a 12-volt source across a 6-ohm resistor, the current is 12/6 = 2 amperes. If you treated E as energy, the units wouldn’t line up to yield amperes, which is why E denotes voltage in this formula.