This equation, called Ohm’s Law, shows the relationship between potential difference, current and resistance:
V = I × R
V is the potential difference in volts, V
I is the current in amperes (amps), A
R is the resistance in ohms, Ω
The equation can be rearranged to find the resistance:
R = V ÷ I
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.