Electric Motor

It is a rotating device (device which rotates or move round and round)

It converts electrical energy into mechanical energy

They are used in Electric fans, Refrigerators, Washing Machines, Mixers,  etc

This is what it looks like

Principle of an electric motor

An electric motor works on the principle that

when a rectangular coil is placed in a magnetic field and a current is passed through it,

a force acts on the coil which rotates it continuously

Construction of Electric Motor

Electric Motor consists of

• Rectangular Coil of Wire ABCD
• A strong horseshoe magnet (or 2 different magnets ) - If we take 2 magnets, North Pole of first magnet faces South Pole of Other Magnet, as shown in figure...
• The coil is placed perpendicular to the magnet as shown in figure
• The ends of coil are connected to split rings - P & Q
  Split rings act as a commutator - which reverses the flow of current in the circuit
• The inner side of the split rings is insulated and attached to the axle (which is free to rotate)
• The external conducting edges of split rings tough two stationary brushes - X & Y
• These brushes are attached to the battery to complete the circuit

Working of Electric Motor

Let's look at the working of an Electric Motor

• When battery is switched on, current flows through coil AB from A to B,
  and Magnetic Field is from North to South...
  So, by Fleming's left hand rule, downward force is applied on AB.
  
  Similarly, upward force is applied on CD.
  Thus, the coil rotates with AB moving down and CD moving up
  
  
• Now, coils AB and CD interchange their positions,
  Since current flows from C to D, and magnetic field from North to South
  CD will receive an upwards force and move upwards
  
  Similarly, AB will move downwards
  So, our coil would do half rotations
  
  
• But, we do not want half rotations, 
  We want full rotation of the coil.
  
  
• So, to do that.. we change the direction of current in the coil when it has done half rotation
  
  
• To change direction of current, we use a commutator.
  A commutator consists of split rings (two rings with some space between them), and brushes attached to the circuit.
  
  
• Now, as the coil rotates, the rings spin with it
  When coil becomes parallel to the magnetic field,
  the brushes X and Y touche the gap between the rings
  and the circuit breaks
  
  
• Now, due to inertia, the ring keeps moving... so the opposite end of the ring is now connected the positive end of wire
  Split ring P is connected to coil CD and split ring Q is connected to coil AB.
  Which reverses the direction of current in the circuit.
  
  
• Now, when CD is on left side and AB is on right side..
  Current in CD becomes reversed i.e. from D to C.
  So, force on CD is downwards and force on AB is upwards
  Thus, the coil keeps rotating
  
  
• This reversing of electric current happens every half rotation
  and the coil continues to rotate until the battery is switched off

Note - If split ring was not used, coil would have rotated half in clockwise direction and half in anticlockwise direction
Hence, the purpose of split ring is to reverse flow of current and make coil rotate in single direction

To write Working of Electric Motor in your Exam Paper, check - NCERT Question 11

How does Commercial Electric Motors increase force produced and power of motors?

They increase force produced and power of motors by

• Using Electromagnet in place of permanent magnet
• Large number of turns of conducting wire(More the turns in wire more the magnetic field)
• Soft iron Core on which coil is wound

Note : The soft iron core on which the coil is wound along with the coils is called an armature .
This enhances the power of the motor.

Note : For your exams,
please write  principle, working, construction of Electric Motor. 
And remember to make the first figure (the one given in NCERT)

Questions

NCERT Question 3 - The device used for producing electric current is called a

1. generator.
2. galvanometer.
3. ammeter.
4. motor.

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NCERT Question 6 (a) - State whether the following statements are true or false.

(a) An electric motor converts mechanical energy into electrical energy.

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NCERT Question 11 - Draw a labelled diagram of an electric motor. Explain its principle and working. What is the function of a split ring in an electric motor?

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NCERT Question 12 - Name some devices in which electric motors are used.

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Questions 2 Page 233 - What is the principle of an electric motor?

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Questions 3 Page 233 - What is the role of the split ring in an electric motor?

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