 |
| The Experiment of Faraday and Henry |
|
|
| Faraday and Henry performed lots of experiments to learn about the connection between electricity and magnetism. The results of these experiments have led to the life styles of todays men, who made life easy by using lots of electrical applications. |
| |
| Some of the experiments are as follows |
| |
 |
| |
| A solenoid is connected to a sensitive galvanometer. On moving a magnet towards a coil, the galvanometer shows a deflection. When the magnet is reversed, the deflection is seen to be in the opposite direction. |
| |
| Once the magnet is stopped, there is no deflection in galvanometer. On moving the magnet faster towards the coil, the deflection is longer. |
| |
| Similar results are obtained when the magnet is kept stationary and the coil is moved. It means that whenever a current was induced in the coil there is a relative motion between the coil and the magnet. The magnitude of the current depended on the strength of the magnet and also on the magnitude of their relative velocity. |
| |
| Similar results were seen when the magnet is replaced by as coil connected to a battery. Even without physically moving the coils a current was shown in the galvanometer only when the switch is on and when the current is put off i.e., when the current is building up in the coil or when it reduced to zero the galvanometer in the other coil showed a charge. |
| |
| This current, which is produced in the coil connected to the galvanometer, is called as induced current. The induced currents direction, when the current builds up in the other coil was opposite to that when the current reduced opposite to that when the current reduced. The deflections were momentarily seen only when the switch was opened and closed. |
| |
| These observations can be summarized in Faraday's laws of electromagnetic induction. |
| |
| (i) Whenever the magnetic flux linked with a circuit changes, an EMF is induced in the circuit, which lasts as long as the change in magnetic flux associated with the circuit continues. |
| |
| (ii) The magnitude of the induced EMF is equal to the rate at which the magnetic flux linked with the circuit changes. |
| |
| Mathematically, |
| |
 |
| |
| Faraday's laws of electromagnetic induction do not say anything about the direction of the current. The direction is given by Lenz's law. |
| |
