# Calculating resistance – Ohm’s Law

The of an can be found by measuring the electric flowing through it and the across it.

This equation, called Ohm’s Law, shows the relationship between potential difference, current and resistance:

voltage = current × resistance

V = I × R

where:

V is the potential difference in , V

I is the current in (amps), A

R is the resistance in ohms, Ω

The equation can be rearranged to find the resistance:

R = V ÷ I

Question

3 A flows through a 240 V lamp. What is the resistance of the lamp?

Resistance = 240 ÷ 3 = 80 Ω

To calculate the resistance of an electrical component, an ammeter is used to measure the current and a voltmeter to measure the potential difference. The resistance can then be calculated using Ohm’s Law.