# why is this?Watch

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#1
When a magnet falls through a coil, why is the induced voltage at its lowest when the magnet is in the centre of the coil? thanks
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5 years ago
#2
(Original post by Mr Tall)
When a magnet falls through a coil, why is the induced voltage at its lowest when the magnet is in the centre of the coil? thanks
The same thing happens if the magnet were stationary and it was a conductor moving in the magnetic field:

The coil cuts the magnets lines of flux and an emf is induced. The magnitude of the emf is determined by the strength of the B-field at any given point, the direction of travel through te field, the velocity of the conductor in relation to the field and the length of the conductor in the field.

The key thing to note here is that the direction of the emf generated in the coil is dependent on whether the B-field is collapsing or growing and the rate of change of the field in relation to the coil.

As the magnet approaches the coil, the induced emf will be in one direction because the coil is entering the magnets B-field which is growing. As the magnet leaves the coil, the induced emf reverses direction because the B-field is now reducing.

When the magnet is in the centre of the coil, the B-field is neither increasing or decreasing. At this point the emf generated must cross the zero threshold since the rate of change of flux is also zero.

If the magnet remains stationary within the core, then no magnetic lines of flux are cut and no emf is generated.
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