Joules Law of Heating – Examples, Definition, Derivation, FAQ’S

Joule’s Law of Heating is a principle in physics that describes the relationship between the electric current flowing through a conductor and the heat produced.

What is Joules Law of Heating?

Joules Law of Heating Formula

The formula for Joule’s Law of Heating describes the heat generated in a conductor due to an electric current flowing through it. The formula is:

where:

• 𝑄 is the heat energy produced (in joules),
• 𝐼 is the electric current (in amperes),
• 𝑅 is the resistance of the conductor (in ohms),
• 𝑡 is the time (in seconds) during which the current flows.

This formula illustrates that the heat produced in the conductor is directly proportional to the square of the current, the resistance, and the time for which the current flows.

Joules Law of Heating Derivation

Let’s derive it step-by-step:

Electric Power: The power 𝑃 dissipated in a resistor is given by: 𝑃=𝐼²𝑅

Heat Energy: Heat energy (𝑄) is the power dissipated over time. So, the heat energy generated in time 𝑡t is: 𝑄=𝑃×𝑡 Substituting the power equation 𝑃=𝐼²𝑅 into this: 𝑄=𝐼²𝑅𝑡

This equation indicates that the heat produced is directly proportional to the square of the current, the resistance of the conductor, and the time the current flows.

Uses of Joules Law of Heating

1. Electric Heating Appliances: Devices such as electric heaters, water heaters, and kettles convert electrical energy into heat energy using resistive elements. This process follows Joule’s Law of Heating. Where the heat produced is directly proportional to the square of the current passing through the element and the resistance of the element itself.
2. Electric Stoves and Ovens: Cooking appliances that operate on electricity, like stoves and ovens, utilize Joule’s Law of Heating to generate the heat necessary for cooking. Electric current flows through resistive heating elements, producing heat according to Joule’s Law, which cooks the food placed in the appliance.
3. Incandescent Bulbs: Traditional incandescent light bulbs produce both light and heat by passing an electric current through a tungsten filament.
4. Electric Welding: In electric welding processes, such as arc welding, intense heat is required to join metals together. Joule’s Law of Heating governs this process, where an electric arc produces heat at the welding point, melting the metal and creating a strong joint.
5. Electrical Resistance Testing: In electrical circuits, Joule’s Law of Heating is utilized to test the resistance of components.
6. Heat Sinks: In electronics, heat sinks use Joule’s Law to dissipate heat from components. They ensure the components don’t overheat by spreading the heat produced due to the flow of current.

Examples for Joules Law of Heating

1. Electric Heaters: Electric heaters convert electric current into heat to warm a space. As current flows through the high-resistance heating element, it produces heat according to Joule’s Law.
2. Fuses: Electrical fuses rely on Joule’s Law to protect circuits. When excessive current flows through the fuse, it generates enough heat to melt the fuse element and break the circuit.
3. Electric Kettles: Electric kettles use heating coils to boil water. When current passes through the coils, the resistance generates heat and warms the water quickly.
4. Incandescent Bulbs: In incandescent light bulbs, the filament heats up and glows as electricity flows through it. The heat produced is proportional to the square of the current, as per Joule’s Law.

FAQ’S

What is the joule theory of heat?

This Theory states that heat results from energy conversion due to the movement of particles. Additionally, it describes how electric currents produce heat in conductors.

What is the SI unit of heat?

The SI unit of heat is the joule (J), which measures the energy transfer from one body to another, indicating the work needed to generate the heat.

Who gave Joule’s law of heating?

James Prescott Joule formulated Joule’s Law of Heating in the 19th century, pioneering the understanding of heat generated by electrical currents flowing through conductors.