Thursday, September 8, 2016

Lenz Law and Electromagnetic Induction

To understand the generated EMF, we have a rule called Lenz rule. This is a fundamental rule and it works basing on law of conservation of energy.

According to the Lenz law, a changing magnetic field produces a induced EMF and induced current in a closed coil. This induced EMF opposes the change in the magnetic flux that creates it.

If we are moving a magnet towards a closed coil, it generates a change in the magnetic field. If you are moving a north pole towards the coil, the current is generated in the closed coil such that it generates another north pole on the face of magnet coming towards it with North Pole so that it opposes the change.

If we are getting south pole of a magnet towards a closed coil, the induced current in that closed coil intern generate another magnetic field with south pole so that it opposes the change in the magnetic flux.

Thus it totally tells us that the induced emf and induced current opposes the change in the magnetic flux that is causing it and that can be shown below in the diagram.

If a bar magnet is coming towards a current carrying coil in the perpendicular plane, an induced EMF is generated. The generated potential difference always oppose the change in the magnetic flux. Thus when north pole of the bar magnet is approaching it, north pole is formed over the surface and anti clock wise current is generated. Even when the north pole is going away from the coil, to oppose that change a south pole is formed on the face of the coil and hence a clock wise induced current is generated there. In that sense, the magnet always experience a acceleration less than the acceleration due to gravity.

If the coil is not a closed coil, there is no induced EMF and hence, the magnet falls through it with an acceleration equal to acceleration  due to gravity.

The magnitude of induced EMF varies even with the variation of the temperature of the coil. If the temperature increases, the resistance of the coil decreases and hence induced emf increases.

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