Electromagnetic Induction

Electromagnetic Induction is the phenomenon of production of induced emf due to change in magnetic flux linked with closed circuit.

The word Electomagnetic induction means inducting electicity by magnetism. The phenomenon is the basis of the working of power generators, transformers, etc.

In 1831, Michael Faraday in England and Joseph Henery in the USA discorved that current. It produced in the loop of wire. If the magnetic field is suddenly moved toward the loop or away from the loop such that the magnetic flux acress the loop changes. The current in the loops last as long as the flux changing.

Magnitc flux

Magnetic flux is the total number of magnetic field lines of force crossing the surface normally”

Unit of magnetic flux is tesla meter^2 which is also called Weber(Wb). It is the scalar quantity. It is also called flux density.

1 weber = 1 Tm^2

Laws of Electromagnetic Induction

(i). Faraday’s laws of Electromagnetic Induction

This laws gives the magnitude of the induced EMF.It state as folllow:-

first law:

“Whenever the magnetic flux associated with the coil changes an EMF is induced in it which last only so long as change in flux is taking place”

Second law:

“The magnitude of induced EMF is equal to the rate of changing of magnetic flux linked with the closed circuit”

(ii). Lenz’s laws of Electromagnetic Induction

This law gives the direction of the induced EMF.

“It states that induced current is such that it opposes the cause which induced it,i.e., it opposes the change in magnetic flux”

Faraday’s Experiment of Electromagnetic induction :

On the basic of several experiment Faraday’s has determined the phemomenon of electomagnetic induction. Some of them are.

Experiment 1: Induced EMF with a stationary coil and moving magnet.

(i) When the N-pole of a strong bar magnet is moved towards the coil, the galvanonometer shows a deflection.

(ii) When the N-pole of the bar magnet is moved away from the coil, the galvanometer shows a direction in opposite direction.

iii) If the above experiment are repeated by brinning the S-pole of the magnet towards or aways from the coil,the direction of the current in the coil is opposite to that obtained in the case of N-pole.

iv) When the magnet is held stationary anywhere near or inside the coil, the galvanometer does not show any deflection.

Experiment 2: Induced EMF with the stationary magnet and moving coil. A similar result is obtained as experiment 1.

(i). When the relative motion between the coil is and the magnet is fast, the deflection in the galvanometer is large and when the relation motion is slow, the galvanometer deflection is small.

(ii). Faster the relative motion between the magnet and the coil,greater is the rate if change magnetic flux linked with the coil and larger is the induced current setup in the coil.

The conclusions of the Faradays Electromagnetic Experiments

(i). Whenever there is a reletive motion between a magnet and a closed conducting loop,electric current appears in the loop,Ithapen because of the change in the magnetic flux.

(ii). Since emf causes current in a circuit,when loop and magnet are brought in relative motion current flows in the loop.This emf is know as induced emf and its magnetude is directly proportional to rate of change of manetic flux through the loop with time.

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Lenz Explanations of Electromagnetic Induction

Lenz has explained the phememenom of Electromagnetic induction by the follow ways

i) When the north pole of the bar magnet is moved towards the closed coil, an induced current in the coil flows in the anticlockwise direction. The face of the coil toward the magnet develops north pole of the magnet towards the coil which is actually the cause of the induced current in the coil.

ii) When the north pole of the magnet is taken away from the closed coil, the induced current in the coil flows clockwise, as seen from the magnet side.

The face of the coil toward the coil developed south polarity and attrats the north pole of the bar magnet,i.e. the motion of the magnet away from the coil is opposed which is really the cause of the induced current.