Electromagnetism is due to the magnetic fields around electric currents. The fields can cause forces with other nearby magnets and these forces can be used to make motors spin.

A wire carrying a current creates a magnetic field. This can interact with another magnetic field, causing a force that pushes the wire at right angles. This is called the motor effect.

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

force = magnetic flux density × current × length

This is when:

*F*is force in newtons (N)*B*is magnetic flux density (magnetic field strength) in tesla (T)*I*is current in amperes – also referred to as amps – (A)- is length in metres (m)

A 2 A current 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.

50 cm = 50 ÷ 100 = 0.5 m

- 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