NCERT Questions

Class 10
Chapter 13 Class 10 - Magnetic Effects of Electric Current

## 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?

Electric Motor 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

### 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, as the coil rotates, the rings spin with it
When coil becomes parallel to the magnetic field,
the brushes X and Y touch the gap between the rings
and the circuit breaks

• And 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

### Function of Split Ring

Function of the split ring is to reverse the flow of current and make coil and axle rotate in the same direction.

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