ABCD is a coil which is placed between the two poles of a permanent magnet. The coil is placed in such a way that the direction of current is perpendicular to the direction of magnetic field.
• Arms of the coil are attached to a split ring; which has two halves P and Q. Arms AB is attached to the half P, and arm CD is attached to the half Q.
• The split rings are touching two static brushes X and Y from which they get electricity supply. The split rings are insulated from inside. An axle is passing through the split rings.
• A battery supplies electric current to the coil. The flow of current is from A to B and C to D.


Working of Electric Motor:
Obeying Fleming’s Left Hand rule, when current passes from A to B; the arm AB of coil moves down. On the contrary, when current passes from C to D; the arm CD moves up.
When the coil makes half a turn, P of split ring touches brush Y and its opposite happens with Q of split ring. As a result, the direction of current gets reversed. This means current now flows D to C and from B to A. This pushes CD down and AB up. As a result, the coil turns continuously.

Electromagnetic Induction: This was first demonstrated by Michael faraday in 1831. When a conductor and magnetic field are in motion relative to each other, electric currents is induced in the conductor. This phenomenon is called electromagnetic induction.

• Take two coils with large number of turns. Let us assume that number of turns in one coil
is 100 and in another coil it is 50.
• Insert a cylinder of a non-conducting material through these coils.
• Connect the coil with 50 turns to a galvanometer.
• Connect the coil with 100 turns to a battery and plug key.

Observation:
• When key is switched on, deflection is seen in galvanometer.
• When key is switched off, deflection is seen in galvanometer; but in opposite direction.
• This shows that whenever there is a change in strength of magnetic field, current is induced in the coil.

Important of Fuse:
• Fuse is an important safety device in household wiring and in electrical appliance.
• Fuse prevents any damage to the circuit and appliance which may happen due to overload.
• Fuse prevents accidental fire which may happen because of short circuit.
Fuse of a particular rating is used with a particular appliance. A fuse with lower rating would result in lot of inconvenience because of frequent need of changing the fuse. A fuse with higher rating would not serve the purpose because it will not melt even if the current exceeds the limit of the device. Hence, a burnt out fuse should be replaced by another fuse of identical rating.

 

ABCD is rectangular coil placed between the two poles of a permanent magnet.
• Arms AB of coil is attached to a ring R1 and arm CD is attached to the ring R2.
• R1 and R2 are insulated from inside and are attached to an axle.
• A brush B1 touches R1 and another brush B2 touches R2.
• A galvanometer is connected to B1 and B2 to show the flow and direction of current in the circuit.


Working of AC Generator:
• AC generator works in Fleming’s Right Hand Rule.
• When coil is rotated within the magnetic field, electric current is induced in it.
• Let us assume that the coil is rotating clocking in this figure. This means, AB is moving up and CD is moving down.
• When AB is moving up, current flows in it from A to B.
• When CD is moving down, current flows in it from C to D.
• After half a turn; relative positions of AB and CD change. Now, CD is moving up hence current is moving from D to C. Similarly, AB is moving down hence current is moving from B to A.
• So, after every half turn the direction of current changes in this generator. This means alternating current is being generated.
Conversion of AC generator to DC generator: For this, a split ring commutator is used in place of two separate rings. A split ring commutator maintains the direction of current in one direction and it becomes a DC generator