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The phenomenon of production of induced emf in one coil due to change of current in a neighbouring coil is called mutual induction. Let us perform an experiment to understand this.
- Place two coils P and S close to each other as shown here
- Connect a battery and a key to the primary coil P and connect the secondary coil S to a sensitive galvanometer G
- Whenever the key is pressed or released the galvanometer shows a deflection
- Now observe the deflection of the galvanometer needle by pressing and releasing the key
- The needle deflects because the current flowing through the primary coil induces a current in the secondary coil
When the key K is pressed, current starts flowing through the coil P and this increases the magnetic flux linked with P.
Since S is very close to P, the magnetic flux linked with S also increases. Thus induced emf, hence induced current is produced in S.
The direction of induced current in S is given by the arrow marked 1, in accordance with Lenz's law.
Similarly, when the key is released, magnetic flux associated with the coils decreases and this gives rise to induced current in the direction shown by the arrow marked 2.
That is mutual induction is the production of induced emf in the secondary coil during the time of make or break of current in the primary coil.
The direction of induced current can be determined by using Fleming's Right Hand Rule.
Stretch the forefinger, the middle finger and the thumb of the right hand, such that they are mutually perpendicular to each other. If forefinger indicates the direction of the magnetic field, the thumb indicates the direction of motion of the conductor, then, middle finger indicates the direction of induced current in the conductor.
The electric generator works on the above explained phenomenon.
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