Explain the underlying principle and working of an electric generator by drawing a labelled diagram. What is the function of brushes?
Solution:
The electric generator converts mechanical energy into electrical energy. The working principle of the electric generator is electromagnetic induction. It generates electricity by rotating a coil in the magnetic field. The figure below shows the construction of a simple AC generator.
In the diagram,
A and B are brushes.
C and D are slip rings.
X is the axle.
G is the galvanometer.
When the axle X is rotated clockwise, MN moves upwards while ST moves downward. The movement of MN and ST in the magnetic field results in the production of electric current due to electromagnetic induction. MN moves upwards, and the magnetic fields act from left to right. Therefore, according to Fleming’s right hand rule, the direction of the induced current will be from M to N along the length MN. Similarly, the direction of the induced current will be from S to T along the length ST. The direction of the current in the coil is MNST. Hence, the galvanometer shows a deflection in a particular direction.
After half a rotation, length MN starts moving downwards while the length ST starts moving upwards. Now, the direction of the induced current reverses to TSNM. Since the direction of the induced current reverses every half rotation, the current induced is known as alternating current.
Function of Brushes
Brushes are kept pressed onto two slip rings separately. The outer ends of the brushes are connected to the galvanometer. Thus, brushes help in transferring current from the coil to the external circuit.
- When does an electric short circuit occur?
Solution:
Listed below are two instances of when a short-circuit can occur:
1) When too many appliances are connected to a single socket or when high power rating appliances are connected to a light circuit, the resistance of the circuit becomes low. As a result, the current flowing through the circuit becomes very high. This condition results in a short circuit.
2) When live wires whose insulation has worn off come in contact with each other, the current flowing in the circuit increases abruptly, which results in a short circuit.