Fleming's Left Hand Rule

The Motor Effect

The motor effect occurs when a conductor carrying a current is placed in a magnetic field that is caused by a secondary magnet. The magnet and the conductor exert a force on each other.

Fleming's Left Hand Rule, figure 1

Electric motors is the application of the motor effect.

A coil of wire carrying a current in a magnetic field tends to rotate.

See the following slides below:

Fleming's Left Hand Rule, figure 2

Fleming's Left Hand Rule, figure 3



Fleming's Left Hand Rule, figure 4

If asked how an electric motor works, ensure you can write the above bullet points.

To increase the strength of an electric motor you need to:

  • Increase the size of the magnets
  • Increase the size of the current
  • Increase the __amount of wire __inside the magnetic field

Fleming’s Left Hand Rule

Fleming came up with a way of showing the orientation of force, current and magnetic field in relation to each other. It requires the use of your left hand.

Fleming's Left Hand Rule, figure 1

Ensure that you know what the fingers and__ thumb__ represent.

Try this: which way is the force acting?

Fleming's Left Hand Rule, figure 2

Answer: into the screen

What is the effect called when a force is produced from placing a conductor inside an external magnetic field?
motor effect

Equation

Magnetic force can be calculated via this equation which is given in your exam:

Force = Magnetic flux density x current x length of wire

F = B x I x l

  • F = Force, Newtons (N)
  • B = Magnetic flux density, Tesla (T)
  • I = Current, Amps (A)
  • l = length of wire in the magnetic field, metres (m)
In Fleming’s left hand rule, label the following in order: Thumb = ? First Finger = ? Second Finger = ?
Force Magnetic field Current