In Ohm's Law, which expression correctly relates voltage, current, and resistance?

• A. I = E x R
• B. E = I x R
• C. E = I / R
• D. E = R / I

Answer: (B)

Voltage is the product of current and resistance. This reflects how much voltage is needed to drive a particular current through a component with a given resistance: if you double the voltage while resistance stays the same, the current doubles; if you increase resistance at the same voltage, the current drops. With E representing voltage, I representing current, and R representing resistance, the direct expression is E = I × R. You can rearrange it to I = E / R, but the form E = I × R directly shows how voltage relates to both current and resistance. The other forms would not give voltage with the correct units or behavior: for example, E = I / R would give a quantity with units of current per resistance, not volts; E = R / I would give resistance per current, also not volts; and I = E × R would imply current equals voltage times resistance, which mismatches the units and the observed relationship.