Electric motors

Electric motors are found almost everywhere; ranging from electrical appliances such as electric drills and vacuum cleaners to toys and lifts!

The motor effect

A wire, carrying an electric current in a magnetic field experiences a force. This force is caused by the motor effect. Every electric motor makes use of the motor effect and thus it is a significant aspect of physics.

As written above, the basic requirements for a wire to produce movement are:

  1. A magnetic field.
  2. A current flowing across the magnetic field.

Demonstrating the motor effect

<Image of figure here>

In the above figure, the copper rod is free to move between the two aluminium supports.

An electric current from the power supply flows through one end of the aluminium support, through the copper rod, and out of the second aluminium support.

The two bar magnets positioned provide a vertical magnetic field.

When the current is switched ON, the copper rod experiences a horizontal force being exerted on it, making it move.

This happens because the magnetic field around the electric current is repelled by the magnetic field of the bar magnets.

How to increase the motor effect?

The motor effect can be increased in two ways:

  1. By increasing the current.
  2. By using magnets with a stronger magnetic field.

How to reverse the force caused by the motor effect?

The force caused by the motor effect can be reversed in two ways:

  1. By reversing the direction of the electric current.
  2. By reversing the direction of the magnetic field.

Fleming’s left hand rule

Fleming’s left hand rule is a rule which gives the relationship between the directions of force, field and current.

In Fleming’s left hand rule, there are three vector quantities:

  1. A magnetic field
  2. An electric current
  3. A force

The magnetic field is vertical, the current and the force are horizontal and at right angles to each other.

Fleming’s left hand rule is used to predict the direction of a force on a current carrying conductor in a magnetic field.

A simple d.c electric motor

A simple electric motor works on direct current (d.c)

It has an axle which rotates when an electric current passes through it.

All electric motors have the following things in common:

  • All electric motors make use of the motor effect.
  • All electric motors have two magnets that provide a steady magnetic field passing through the coil.
  • All electric motors also have a split ring commutator through which the electric current reaches the coil.
  • All electric motors have a coil of wire that acts as an electromagnet when a direct current is passed through it.
  • All electric motors have two brushes which act as springy wires that press against the two metal sections of a commutator.

How does an electric motor work?

Here is an explanation of how an electric motor works:

  1. A current flows into one of the brushes, into the coil of wire and out of the second brush.
  2. As the current flows through the coil of wire, it becomes an electromagnet.
  3. At this point, the upper side of the coil of wire becomes the north pole (and the lower side, the south pole)
  4. The north pole of the coil is attracted to the south pole of the permanent magnet.
  5. This causes the coil of wire to move anticlockwise, and attain a vertical position.
  6. Here, the current flows in the reverse direction as the brush connections to the two halves of the commutator are reversed.
  7. The uppermost side of the coil of wire is again the north pole now, and it again turns 1800

How to make an electric motor more powerful?

Electric motors can be made more powerful by:

  1. Increasing the strength of the electromagnet.
  2. Increasing the number of turns on the solenoid.
  3. Using more powerful permanent magnets.

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