Ohm's Law Resistor Power
Ohm’s Law: Current and Resistor Power
Ohm’s law is the foundation of circuit analysis. This worksheet finds the current through a resistor at a given voltage and the power it dissipates as heat — the number that sets the required resistor wattage rating.
Ohm’s law is I = V/R and the dissipated power is P = VI (equivalently I²R or V²/R).
Inputs
V := 12 V=12 V
R := 100 Ohm=100 Ω
Current and power
I := V/R=0.12 A
P := V·I=1.44 W
Results
Choose a resistor whose power rating comfortably exceeds the dissipation shown (a common rule is to rate it at twice the calculated power for headroom). The current also feeds wire-gauge and fuse selection upstream.
Assumptions & limitations
- Ideal ohmic resistor, constant resistance.
- DC or RMS values; steady state.
- Resistance not corrected for temperature rise.