1. Why Current Produces Heat
When electric current flows through a conductor, electrons move through the material and collide with atoms. These collisions make the atoms vibrate more, and this vibration appears as heat.
This is why wires get warm when current flows through them.
1.1. Energy Lost in Collisions
As electrons drift through the conductor, some of their energy is transferred to the atoms during collisions. This energy transfer increases the temperature of the conductor.
2. Joule’s Law of Heating
Joule’s law gives the amount of heat produced in a conductor when current flows for a certain time.
2.1. Statement of Joule’s Law
Heat produced in a conductor is directly proportional to:
- the square of the current \((I^2)\)
- the resistance of the conductor \((R)\)
- the time for which current flows \((t)\)
2.1.1. Formula for Heat Produced
\( H = I^2 R t \)
This formula shows that even a small increase in current produces a large increase in heat because of the square term.
3. Power and Heating
The heating effect is closely linked to the electrical power consumed in the conductor.
Power is the rate at which electrical energy is converted to heat.
3.1. Using Power Formulas
\( P = I^2 R \)
\( P = VI \)
\( P = \dfrac{V^2}{R} \)
All these forms can be used depending on which quantities are known.
4. Applications of Heating Effect
The heating effect is used intentionally in many devices. The idea is simple: when a high-resistance element carries current, its temperature rises quickly.
4.1. Common Examples
- Electric heaters
- Toasters
- Irons
- Electric bulbs (filament heating)
In all these devices, materials with high resistivity are used so they heat up easily.
5. Example to Visualise Heating
A thin wire of high resistance gets much hotter than a thick wire when the same current flows through both. This is because heating depends on resistance—more resistance means more heat produced for the same current.