Which expression correctly represents Ohm's law relating voltage, current, and resistance?

• A. P = I V
• B. V = I R
• C. I = V / P
• D. R = V / I^2

Answer: (B)

Ohm's law describes how voltage, current, and resistance are connected in a simple conductor: the voltage across a component equals the current through it times its resistance, written as V = IR. This means that if you fix the resistance and increase the voltage, the current rises proportionally; if you fix the voltage and increase the resistance, the current drops. A handy check is a resistor with 5 volts across it and 1 ohm of resistance gives a current of 5 A, because 5 V = (5 A)(1 Ω). The units line up: volts equal amperes times ohms.

The other forms mix in different quantities or rearrange in ways that don’t express the V, I, and R relationship directly. For example, P = VI is a valid relation involving power, voltage, and current, but it’s not the form that directly ties voltage to current and resistance. Expressions like I = V/P or R = V/I^2 don’t represent the standard Ohm’s-law relation among V, I, and R.