Resistance is a property of a material that opposes the flow of electric current. Think of it like a traffic jam for electrons – the tighter the jam, the harder it is for the electrons to move. The unit of resistance is the ohm (Ω).
When current flows through a resistor, electrical energy is converted into other forms of energy. The most common conversion is to heat energy, but it can also become light, sound, or mechanical motion in certain devices. The basic relationship is:
\$P = I^2 R\$ (power dissipated as heat)
\$P = IV\$ (power in general)
\$P = \frac{V^2}{R}\$
The heat produced can be visualised as the resistor “getting warm” or even glowing if the power is high enough. This is why a light bulb filament gets hot – it is a resistor designed to produce light and heat.
Not all energy ends up as heat. In a light bulb, some energy becomes visible light. In a motor, electrical energy is converted into mechanical motion. Even a speaker turns electrical signals into sound waves. The key idea is that the resistor or component is a site where energy is transformed and then released into the surroundings.
When you push the button on a toaster, current flows through the heating elements (tiny resistors). The elements resist the flow, converting electrical energy into heat, which then browns your bread. The heat also warms the surrounding air, showing the energy transfer to the environment.
| Formula | Description |
|---|---|
| \$P = I^2 R\$ | Power dissipated as heat in a resistor. |
| \$P = IV\$ | General power equation for any component. |
| \$P = \dfrac{V^2}{R}\$ | Power expressed in terms of voltage and resistance. |