Resistance is a measure of how much a material opposes the flow of electric current. Think of it as a traffic jam for electrons.
Mathematically, \$R = \dfrac{V}{I}\$, where \$V\$ is voltage (volts) and \$I\$ is current (amps).
Units: ohms (\$\Omega\$).
Imagine water flowing through a pipe. The pipe’s diameter and roughness determine how hard it is for water to move. A narrow, rough pipe is like a material with high resistance.
In a typical 12 V battery circuit, a 3 Ω resistor will allow a current of \$I = \dfrac{V}{R} = \dfrac{12}{3} = 4\$ A.
| Component | Resistance (Ω) |
|---|---|
| Copper wire (1 m, 1 mm²) | ~0.017 |
| Aluminium foil (1 m, 1 mm²) | ~0.028 |
Resistance tells us how much a material hinders current flow. The higher the resistance, the lower the current for a given voltage.