Power Dissipation Calculator

Power Dissipation in Resistors

When current flows through a resistor, electrical energy is converted to heat. Power dissipation quantifies this heat loss per unit time and is essential for selecting resistor wattage ratings and thermal management.

Formulas

Joule heating gives three equivalent expressions:

$$ P = V I $$ $$ P = I^2 R $$ $$ P = \frac{V^2}{R} $$

Use whichever pair of values you know. All three yield the same power in watts when voltage, current, and resistance are consistent with Ohm's law.

Practical Notes

Every resistor has a maximum power rating. Operating above that rating causes overheating and failure. In series circuits, current is shared but power splits by resistance. In parallel circuits, voltage is shared and lower resistance paths dissipate more power.

Frequently Asked Questions

What is power dissipation?

Power dissipation is the rate at which electrical energy is lost as heat in a component, measured in watts.

Which formula should I use?

Use P = VI when you know voltage and current, P = V²/R when you know voltage and resistance, and P = I²R when you know current and resistance.

What happens if dissipation exceeds the resistor rating?

The resistor overheats. Prolonged overload can damage the component, nearby parts, or the circuit board.

Is dissipated power always undesirable?

Usually it is wasted energy, but electric heaters intentionally use resistive dissipation to produce heat.

How do I find heat energy from power?

Multiply power in watts by time in seconds. Energy in joules equals power times time.

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Power Dissipation in Resistors

Formulas

Practical Notes

Frequently Asked Questions

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