What is Electrical Resistance?

In short

Electrical resistance is the opposition a conductor offers to the flow of electric current through it. It is measured in ohms ( $\Omega$ ).

In simple words

The resistance of a wire is $R = \rho\dfrac{l}{A}$ , where $\rho$ is the resistivity of the material, $l$ is the length and $A$ is the cross-sectional area. A longer wire has more resistance. A thicker wire has less. For a fixed temperature, many conductors obey Ohm's law, $V = IR$ . The resistance of a metal rises as it gets hotter.

Example

A copper wire has $\rho = 1.7 \times 10^{-8}\ \Omega\,\text{m}$ , a length of $10\ \text{m}$ and a cross-section of $1.0\ \text{mm}^2 = 1.0 \times 10^{-6}\ \text{m}^2$ . Its resistance is $R = 1.7 \times 10^{-8}\ \Omega\,\text{m} \times \dfrac{10\ \text{m}}{1.0 \times 10^{-6}\ \text{m}^2} = 0.17\ \Omega$ .

Also searched as: resistance of a wire, resistance wire, the resistance of a wire.