The Motor Effect (AQA GCSE Physics): Revision Note

The Motor Effect

Higher Tier Only

• The motor effect occurs when:

A wire with current flowing through it is placed in a magnetic field and experiences a force

• This effect is a result of two interacting magnetic fields

  • One is produced around the wire due to the current flowing through it

  • The second is the magnetic field into which the wire is placed, for example, between two magnets

• As a result of the interactions of the two magnetic fields, the wire will experience a force

The magnetic field between opposite poles of magnets interacts with the magnetic field produced around a current-carrying wire

The motor effect is a result of two magnetic fields interacting to produce a force on the wire

Factors Affecting Force

• The size of the force exerted by the magnetic fields can be increased by:

  • Increasing the amount of current flowing through the wire

    • This will increase the magnetic field around the wire

  • Using stronger magnets

    • This will increase the magnetic field between the poles of the magnet

  • Placing the wire at 90^o to the direction of the magnetic field lines between the poles of the magnet

    • This will result in the maximum interaction between the two magnetic fields

• Note: If the two magnetic fields are parallel there will be no interaction between the two magnetic fields and therefore no force produced

Calculating Magnetic Force on a Current-Carrying Conductor

Higher Tier Only

• The size of the force acting on a current-carrying wire in a magnetic field can be calculated using the equation:

• Where:

  • F = force acting on current-carrying wire in newtons (N)

  • B = magnetic flux density (which is the strength of the magnetic field) in tesla (T)

  • I = current flowing through the conductor in amps (A)

  • L = length of the conductor that is in the magnetic field in metres (m)

Force on a current-carrying conductor (directed into the page)