Electrical Power
Power dissipated in an electrical component.
Formula
Variables
Example
A 3 A current at 12 V dissipates P = 12·3 = 36 W.
How it works
Electrical power tells you how quickly an electrical device converts energy into other forms such as heat, light, or motion. It is found by multiplying the potential difference by the current because each coulomb of charge loses V joules of energy and I coulombs pass each second, so the energy transferred per second is VI. Using Ohm’s law, V = IR, gives the equivalent form I^2R for situations where current and resistance are known instead of voltage.
When to use it
Use this formula when you need the power used by a circuit component, such as a resistor, lamp, heater, or motor. It is also useful for checking whether a device is drawing a safe amount of power or to find the heat produced in a resistor.
Worked example, step by step
A resistor has a current of 2 A flowing through it and a resistance of 5 Ω. P = I^2R P = 2^2 × 5 P = 4 × 5 P = 20 W So the resistor dissipates 20 watts of power.
Common mistakes to avoid
- Using volts, amps, and ohms without keeping the units consistent
- Forgetting that I^2R means the current must be squared before multiplying by resistance
- Using P = VI when the voltage given is not across the component of interest
Did You Know?
P = VI explains why power lines run at extremely high voltage — it lets them carry power with less current and less loss.
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