Joule's Law states that the heat developed within a conductor by an electric current is directly proportional to the square of the current flowing through it, the resistance of the conductor, and the amount of time current flows. This is one of the basic laws that describes how electrical energy can be converted to heat.

Key Features:

• Equation: H = I²RT. Where H = heat, I = current, R = resistance, and T = time.
• The basic principle: The greater the current, or resistance, the more heat will be generated, and it can show some simple electrical and thermal behavior.
• Operation: Joule's Law is used where electrical energy is generated into heat in electrical heating devices and initiated processes like welding; it is also used in fuses and thermal protection systems.

Joule's Law is important for the electrical engineer to be able to produce a safe and efficient electrical circuit. It is used by the electrical engineer to make predictions of how much heat a metal conductor would produce with a given voltage, etc., for the purpose of preventing overheating, material failure, or fire hazards. A good example is electric heaters and resistance welding.