Which equation is Ohm's Law relating voltage, current, and resistance?

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

Answer: (A)

Voltage, current, and resistance are tied together by a simple proportional rule: voltage equals current times resistance. This form shows directly how much voltage is needed to push a given current through a resistor with a certain opposition. For example, if 2 A flows through a 3 Ω resistor, the voltage across it is 2 × 3 = 6 V. In SI units, volt = ampere × ohm, so the relationship V = IR makes sense both conceptually and numerically.

Other expressions mix in different quantities. P = VI describes electrical power, not the direct voltage–current–resistance link. I = P × R doesn’t reflect the standard relationship among these three quantities, and R = V × I would give the wrong units and is not how resistance is defined. The correct ways to relate the three are V = IR, I = V / R, and P = VI.