Calculating the size of the force

To calculate the force on a wire carrying a current at right angles to a magnetic field, use the equation:

force on a conductor (at right angles to a magnetic field) carrying a current = magnetic flux density × current × length

This is when:

  • force is measured in newtons (N)
  • magnetic flux density (magnetic field strength) is measured in tesla (T)
  • current is measured in amps (A)
  • length is measured in metres (m)

Example

2 A flows through a 50 cm wire. Calculate the force acting on the wire when it is placed at right angles in a 0.4 T magnetic field.

First convert the units:

50 cm = 50 ÷ 100 = 0.5 m

Then substitute the values into the equation:

force on a conductor carrying a current = magnetic flux density × current × length

force = 0.4 × 2 × 0.5

force = 0.4 N

Question

A 5.0 cm wire carries a current of 0.75 A. Calculate the force acting on the wire when it is placed at right angles in a 0.60 T magnetic field.

5.0 cm = 5 ÷ 100 = 0.050 m

force on a conductor carrying a current = magnetic flux density × current × length

force = 0.60 × 0.75 × 0.050

force = 0.0225 N