How to Calculate Ohm's Law
What is Ohm's Law?
Ohm's Law states that voltage (V) equals current (I) multiplied by resistance (R): V = IR. It is the foundation of electrical circuit analysis. Power (P = VI = I²R = V²/R) describes the energy converted per second.
Step-by-Step Guide
- 1Identify any two known values: voltage (V), current (A), or resistance (Ω)
- 2Rearrange: V = IR, I = V/R, R = V/I
- 3Calculate power: P = V × I = I²R = V²/R
- 4Apply units: Volts (V), Amperes (A), Ohms (Ω), Watts (W)
Worked Examples
Input
12V battery, 4Ω resistance
Result
I = 3A, P = 36W
I = 12/4 = 3A, P = 12×3 = 36W
Input
120V outlet, 10A circuit
Result
R = 12Ω, P = 1,200W
A typical 1,200W microwave
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