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

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  • 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.


  • 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.


  • 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.


  • 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.

Physics Class 10 Electricity Generator

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