Joule’s law

Definition

Joule's law states that the rate of heat production by an electric current in a conductor is directly proportional to the square of the current, the resistance of the conductor, and the time. Mathematically, it is expressed as $P = I^2R$ where $P$ is power, $I$ is current, and $R$ is resistance.

5 Must Know Facts For Your Next Test

1. Joule's law can be used to calculate the power dissipated as heat in resistors.
2. The formula $P = I^2R$ indicates that power increases with the square of the current.
3. In a series circuit, all resistors share the same current, so Joule's law applies directly using that common current.
4. In a parallel circuit, each resistor has its own current which must be calculated separately before applying Joule's law.
5. Joule's law helps explain why resistors in electronic devices get hot when a current flows through them.

Review Questions

• What does Joule's law state about heat production in a conductor?
• How does power dissipation change with respect to current according to Joule's law?
• How would you apply Joule’s law to determine the power dissipated in a resistor within a parallel circuit?

Related terms

Ohm’s Law: Defines the relationship between voltage ($V$), current ($I$), and resistance ($R$) as $V = IR$.

Resistor: A component that resists the flow of electric current, causing energy dissipation primarily as heat.

Power: The rate at which electrical energy is transferred by an electric circuit; measured in watts (W).