Question

Explain the underlying principle and working of an electric generator by drawing a labelled diagram. What is the function of brushes?

Answer 1

• An electrical generator is a device that converts mechanical energy to electrical energy.
• The generation of alternating currents (ac) is based on the phenomenon of electromagnetic induction.

Principle:-

• Current is induced in a loop through a change in its orientation or a change in its effective area.
• Induced emf is produced either by changing θ or by changing the area vector.
• Direction of current is given by Fleming’s right hand rule.
• Direction of the current in the circuit changes by the up and down movement of the loops.

Construction:-

• It consists of a rectangular coil ABCD.
• It consists of 2 poles (north and south) of a magnet in order to have uniform magnetic field.
• There is a coil which is made up of large number of turns and is of rectangular shape also known as armature.
• The armature is connected to 2 slip rings.
• Slip rings helps in electrical contact with the brushes. It does not change current direction.
• The slip rings provide a continuous connection with the wire around the armature.
• These slip rings are attached to carbon brushes.
• The rectangular coil is capable of rotating about an axis which is perpendicular to the magnetic field.
• The axis of rotation is known as axle.

Working:-

• The generator ABCD is at horizontal position. And if it is rotated in anti-clockwise direction between the two poles of the magnet.
• As the coil rotates in the anticlockwise direction, the side AB of the coil moves cutting down the magnetic lines of force near N-pole of the magnet and the side CD moves up cutting down the lines of force near the S-pole of the magnet.
• As a result current is induced in the sides of AB and CD of the coil.
• By applying Fleming’s left hand rule, the direction of current is in the direction B to A and D to C respectively.
• The induced currents in the two sides of the coil are in the same direction, and as result effective induced current is generated in the direction of BADC.