# A coil is connected to a voltmeter. A bar magnet, initially held above the coil, is left to fall into the coil. Explain why the voltmeter shows a reading. How will the reading of the voltmeter be affected if the magnet is dropped from a greater height?

As the bar magnet enters and exits the coil, there is a change in magnetic flux linkage through the coil. According to Faraday's law, an EMF is induced across the coil that is proportional to the rate of change of magnetic flux linkage. EMF=-N*dΦ/dt, where N is the number of turns of the coil, Φ is the magnetic flux and t is time. This EMF is measured by the voltmeter. If the magnet falls from a greater height, it will be accelerating downwards for a longer time. Thus, its speed will be greater when it reaches the coil. Hence, the rate of change of magnetic flux linkage in the coil will be greater. In other words, more magnetic field lines of the magnet will be cutting the coil per second. This will result in a greater induced EMF and the reading of the voltmeter will be greater.

Answered by Andrea A. Physics tutor

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