Calculating resistance

You should understand the relationship between potential difference, current and resistance.

Why do we get resistance?

An electric current flows when electronselectrons: Sub-atomic particles, with a negative charge and a negligible mass relative to protons and neutrons. move through a conductor. The moving electrons can collide with the atoms of the conductor. This makes it more difficult for the current to flow, and causes resistance.

Electrons collide with atoms more often in a long wire than they do in a short one. A thin wire has fewer electrons to carry the current than a thick wire. This means the resistance in a wire increases as:

• the length of the wire increases
• the thickness of the wire decreases

Calculating resistance

Resistance is measured in ohms, Ω.

You can calculate resistance using this equation:

potential difference (volt, V) = current (ampere, A) × resistance (ohm, Ω)

Check that you understand the relationship between potential difference, current and resistance using this activity.