What does Ohm's law express in an electrical circuit?

• A. V = I × R
• B. P = V − I × R
• C. V = I / R
• D. I = V × R

Answer: (A)

Ohm's law describes how voltage, current, and resistance relate in a circuit: the voltage across a conductor equals the current through it multiplied by the conductor’s resistance, written as V = I × R. This means current through a resistor scales with both the voltage across it and its resistance. If you know two of the quantities, you can find the third. For example, with a 5-ohm resistor carrying 2 amperes, the voltage across it is 10 volts.

This form is the correct way to connect the three variables. The other expressions mix in different concepts or use incorrect operations: power is defined as P = V × I (not P = V − I × R), and current relates to voltage and resistance by I = V / R (not V = I / R or I = V × R). Understanding V = I × R lets you quickly solve for any one variable when the other two are known.