Which equation represents Ohm's Law for basic circuit sizing?

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

Answer: (A)

Ohm's Law shows how voltage, current, and resistance relate in a circuit. The direct form you use for sizing is the voltage across a component equals the current through it times its resistance: V = I × R. This tells you how much voltage is needed for a given current through a resistance, or conversely how much current flows for a given voltage and resistance.

The other expressions are just rearrangements: current is V divided by R, and resistance is V divided by I. P = V × I is about power, and while you can derive P = I^2R or P = V^2/R from Ohm's Law, it’s not the fundamental relationship used for the sizing itself.