Electric resistance

Home learning focus

Learn about electric resistance as well as conductors and insulators.

This lesson includes:

  • one video about current and resistance

  • an activity to test your knowledge

Learn

Watch this video that explains electric resistance, how it's calculated and how it affects current flow.

What is resistance?

All the wires and components in a circuit will somewhat restrict the flow of current through them. This is called electric resistance.

The unit of resistance is the ohm, and it has the symbol Ω (an uppercase Greek letter omega). For example, a 2 Ω component has a greater resistance than a 1 Ω component, and will reduce the flow of current through it more effectively.

Resistance affects the current in a circuit.

Calculating resistance

To find the resistance of a component, you need to measure:

  • the potential difference across it
  • the current flowing through it

The resistance is the ratio of potential difference to current. We use this equation to calculate resistance:

resistance = potential difference ÷ current

For example, if a bulb has a p.d. of 1.5 V and has 2 A flowing through it, then the resistance of the bulb will be 0.75 Ω.

Conductors and insulators

Different materials have different resistances. The resistance of a material is affected by how well an electric current can pass through it:

  • an electrical conductor has a low resistance
  • an electrical insulator has a high resistance

You can easily find out which materials are conductors and which are insulators using a simple circuit. You set up a series circuit with a cell, lamp and wires. Leave a gap in the circuit between two of the wires. Then connect the two wires using pieces of each material and see if the lamp lights up:

  • it will light up if the material is a conductor
  • it will not light up if the material is an insulator

The brightness of the bulb will also be affected, depending on how many components or which material is in the circuit.

Practise

Practise

There are lots of ways to try out your science skills.

Activity

Test what you have learned about electric conductors with this downloadable worksheet from Twinkl.

Electric conductors worksheet

There's more to learn

Have a look at these other resources around the BBC and the web.

KS3 Physics
11-14 Physics
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