Concepts of Physics

IIT JEE Physics (1978-2018: 41 Years) Topic-wise Complete Solutions

Inducing Current without a Magnet

Introduction

Faraday's law of electromagnetic induction is generally demonstrated by movement of a magnet in the vicinity of a coil. This demonstration shows electromagnetic induction without using a magnet.

Apparatus

Galvanometer, battery, long nail, enameled copper wire

Procedure

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Take a long nail and wind two coils side by side over it, as shown in figure. The coils should have about 100~turns of thick enamelled copper wire. Connect one coil to a battery through a switch. This coil is called the first coil or the primary coil. Connect the other coil to a galvanometer or galvanoscope. This coil is called the second coil or the secondary coil.

Turn on the switch while looking at the galvanometer. You will see that the needle of the galvanometer gets deflected and then immediately return to the zero mark, even while the switch is on. Now, turn off the switch. This time, the needle will get deflected in the opposite direction and then it will immediately return to the zero mark. The deflections in the galvanometer show that a current flows for a short while through the secondary.