Calculating resistance – Ohm’s Law
Current - the charge passing a point per second.
Voltage/potential difference - the energy transferred per coulomb of charge.
The The opposition in an electrical component to the movement of electrical charge through it. Resistance is measured in ohms. of an A device in an electric circuit, such as a battery, switch or lamp. can be found by measuring the electric Moving electric charges, eg electrons moving through a metal wire. flowing through it and the The potential difference (or voltage) of a supply is a measure of the energy given to the charge carriers in a circuit. Units = volts (V). This is the voltage between two points that makes an electric current flow between them. across it.
This equation, called Ohm’s Law, shows the relationship between potential difference, current and resistance:
V = I × R
where:
V is the potential difference in Unit of voltage. For example, the voltage across the lamp was 6 volts (V)., V
I is the current in Unit of current, eg the current in the bulb is 4 amps or amperes (A). (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.
