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 carrying a current = magnetic field strength × current × length

F = B ~ I ~ l

This is when:

  • force (F) is measured in newtons (N)
  • magnetic field strength (B) in measured in tesla (T)
  • current ( I) is measured in amps (A)
  • length (l) is measured in metres (m)

Example

A 50 cm wire carries a current of 2 A. 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 = \frac{50}{100} = 0.5~m

Then substitute the values into the equation:

force on a conductor carrying a current = magnetic field strength × 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 field strength × current × length

force = 0.60 × 0.75 × 0.050

force = 0.0225 N