Photograph E shows a rechargeable torch. When a student shakes the torch, the magnet moves through the coil and back again. This induces a voltage across the ends of the coil. The voltage is used to provide current to recharge the battery. (a) Explain why a voltage is induced (b) State one way to increase this voltage

a) according to Faraday's law , b) creating a faster movement, placing more turns on coil

Explanation:

a) The voltage is induced in the coil by the relative movement between it and the magnet, therefore according to Faraday's law

           E = - d (B A) / dt

In this case, the magnet is involved, so the value of the magnetic field varies with time, since the number of lines that pass through the loop changes with movement.

This voltage creates a current that charges the battery

b) There are several ways to increase the voltage

* creating a faster movement, can be done by the user

* placing more turns on the coil, must be done by the manufacturer

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