Faraday (& Henry) Experiment
Description:
Faraday’s experiment was conducted in two parts −
Coil and Magnet
In this experiment there is a coil which is connected to a galvanometer / amperemeter at its end which indicates the presence of current in the coil. A magnet is placed on the axis of the coil as shown in figure.
The magnet is moved along the axis and the ampere-meter is observed. The results found are −
When the magnet is stationary, current in the coil is zero.
When the magnet moves with a velocity ‘V’ towards the coil, there is a current ‘i’ induced in the coil.
When the magnet stops near the coil, current in the coil is zero.
When the magnet moves with a velocity ‘V’ away from the coil, there is a current ‘i’ induced in the coil but in opposite direction.
When the magnet stops again, current in the coil is zero.
By analyzing the above observation, it was concluded that necessary condition for current to flow in the coil was the motion of magnet.
Two coils
In this experiment there is a coil which is connected to a power source such as battery and there is a switch in the circuit as shown in figure. There is another coil placed on the same axis. The second coil does not have a power source, instead a galvanometer / ampere-meter is connected at its end which indicates the presence of current in the coil.
The following observations were made −
When the switch is open, current in the first coil is zero and current in the secondary coil is zero.
When the switch is closed, current in the first coil increases from 0 to ‘i’ and current in the secondary coil increases in opposite direction.
When the switch remains closed, current in the first coil remains ‘i’ and current in the secondary coil becomes zero.
When the switch is again opened, current in the first coil reduces to zero and current in the secondary coil increases from 0 to ‘i’.
When the switch is open for some time, current in the first coil remains zero and current in the secondary coil come back to zero.
By analyzing the above observation, it was concluded that necessary condition for current to flow in the second coil is change in current in the first coil.