Experiment: Parallel Current Carrying wires

Parallel current carrying wires demonstrate that a wire has a magnetic field when there are electrons running through it. These magnetic fields can interact with one another. In this experiment we will see this first hand.

After today you will:

  • Conduct a quantitative investigation to demonstrate the interaction between two parallel current carrying wires
  • Analyse the interaction between two parallel current-carrying wires and determine the relationship between the International System of Units (SI) definition of an ampere and Newton’s Third Law of Motion


As we saw in the 𝐹 = 𝑙𝐼𝐡sinπœƒ lesson, a current carrying conductor creates a magnetic field when a charge is passed through it. Therefore, you would expect that putting two current carrying conductors together, we would expect to see the wires attract or repel one another. If the current’s are running in the same direction the wires will be attracted together. If they run in opposite directions the wire will be repelled apart.

We can use our right hand to predict the magnetic field around a wire. Our thumb points in the direction of conventional current, from positive to negative. The way our fingers wrap around the wire is the direction the magnetic field goes around the current carrying conductor.

We can use the following formula to predict the strength of the force acting on the wires.

𝐹/𝑙 = (πœ‡0/2πœ‹)(𝐼1𝐼2)/π‘Ÿ

  • F : Force acting on the entire wire (N)
  • πœ‡0 : permeability of free space
  • 𝐼1 : Current running through one of the wire (A)
  • 𝐼2 : Current running through the other wire (A)
  • r : The distance between the two wires (m)



Question 1.

What do you hypothesis would happen if you ran two current carrying conductors in the same direction?

Question 2. [5 mark]

Two wires, spaced 30 cm apart, have 3 A running in both wires in opposite directions. The wires are 2 m long.

a) Will the wires be repelled or attracted [1 mark]

b) What magnitude of force will be acting on each of the wires [2 marks]

c) If both of the wires which are 2 m long, weigh 2kg, what acceleration will they experience if allowed to move. [2 marks]

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Question 1.

The wires would be attracted together. If we imagine the magnetic field around the wires, we know they will run in the same directions. As a result, the fields will be acting to attract one another.

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