In Ohm's law, which equation correctly expresses current?

• A. Current = Voltage / Resistance
• B. Voltage = Current × Resistance
• C. Resistance = Voltage / Current
• D. Power = Voltage × Current

Answer: (A)

Understanding how current relates to voltage and resistance is what Ohm's law captures. The direct way to express current is I = V / R. This form shows that current increases as voltage increases and decreases as resistance increases, with the units of amperes (I) coming from volts per ohm.

Why this is the best form: it gives current explicitly in terms of the other two quantities, making it easiest to solve problems where you know voltage and resistance and want the resulting current. If you rearrange the equation to V = I × R, you’re expressing voltage in terms of current and resistance, not current itself. Similarly, R = V / I expresses resistance, not current, and P = V × I describes power, which is a different quantity altogether.

So the direct current form, I = V / R, is the most straightforward expression of current in Ohm's law.