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Question 16

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

Answer

An electric generator is an electric device used to convert mechanical energy (kinetic energy) into electrical energy (electricity).

Principle: Electric generator based on the principle of an electromagnetic induction. When the coil of an electric generator rotates in a magnetic field it induces the current flows in the circuit connected with the coil.

There are two types of electric generator:

i. AC generator
ii. DC generator

AC generator: AC generator is a device that converts mechanical energy into electrical energy in the form of alternating current or AC.

DC generator: DC generator is a device that converts mechanical energy into electrical energy in the form of direct current or AC.

AC Generator Construction: The components of AC generator are:

  1. Armature: Large number of turns of insulated copper wire wound over a soft iron core form  armature coil (ABCD).

  2. Strong field magnet: A strong permanent magnet or an electromagnet whose poles are cylindrical in shape is a field magnet. The armature coil rotates between the poles. The uniform magnetic field is provided by the field magnet perpendicular to the axis of rotation of the coil.

  3. Slip Rings: Two brass slip rings R1 and R2 are connected to the two ends of the armature coil. Rings rotate with the armature coil. Rings R1 and R2 are at different heights.



  4. Brushes: These brushes are connected to the external circuit across which the output is obtained. Two carbon brushes (B1 and B2), are pressed against the slip rings. The brushes are fixed while slip rings rotate along with the” armature.

Working: The armature coil ABCD when rotates in the magnetic field that is provided by the strong field magnet, it cuts the magnetic field lines.therefore, the change in  magnetic field produces induced current in the coil. The direction  of the induced current in the coil is determined by Fleming's right hand rule.

The current flows out through the brush B1 and brush B2 is in the opposite direction. The brush B1 in one direction in the first half of the revolution and by the brush B2 in the next half revolution in the opposite direction. This process is repeated several times. Hence, induced current produced is of alternating current.

DC generator or Dynamo Construction:

  1. Armature coil. Large number of turns of insulated copper wire wound over iron core in a form of a rectangle coil.

  2. Strong field magnet. Strong field magnets provide a strong magnetic field. When an armature coil is kept between two pole pieces of a strong magnet.

  3. Split-ring Type Commutator consists of two halves (R1 and R2) of a metallic ring. Two halves of the ring are connected to the two ends of the armature coil.

  4. Carbon brushes B1 and B2 are pressed against the commutator.

  5. The output is shown by the glowing bulb connected across the carbon brushes.

Working: When the coil of d.c. the generator rotates in the magnetic field, potential difference is induced in the coil. This induced potential difference gives rise to the flow of current through the bulb and therefore the bulb glows.

In d.c. generator, current flows  in the circuit in the same direction for long as the coil rotates in the magnetic field. This is one brush is always in contact with the arm of the armature moving up and the other brush is in contact with the arm of the armature moving downward in the magnetic field.

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