A worked example
A 12V supply across a 4Ω resistor draws 3A of current and dissipates 36W of power.
Frequently asked questions
What's the relationship between Ohm's Law and power?
Power (in watts) is how much energy a circuit component uses per second — P = V × I. Since V = I × R, you can also express it as P = I²R or P = V²/R depending on which two quantities you know, but they all derive from the same underlying relationship.
Does Ohm's Law apply to all materials?
Only to 'ohmic' materials — those where resistance stays constant regardless of voltage and current. Many real-world components (LEDs, diodes, transistors) are non-ohmic and have resistance that changes with operating conditions, where Ohm's Law breaks down as a simple model.