Electromagnetic induction is the process by which a changing magnetic field in a conductor induces a current in another conductor. Two ways by which electric conductors can be induced in a coil are:
(i) By moving the coil in a magnetic field.
(ii) By changing the magnetic field around the coil.
Place two coils side by side as shown in Fig. Connect coil A to a battery through a switch and coil B to a centre-zero galvanometer. Observe what happens when the current is switched on in the coil A. You will see that a current is induced in coil B, even though the coils are not moving. When you switch on coil A it produces a magnetic field around the coil B. The effect is just the same as pushing a magnet quickly into the coil B. An induced current flows for a moment in coil B. The needle of the galvanometer connected to the second coil B instantly jumps to one side and just as quickly returns to zero, indicating a momentary current in the coil . When the magnetic field is steady, the current stops flowing. When you switch off coil A, the magnetic field stops quickly. This is the same as pulling a magnet out of coil B, and an induced current flows in the coil in an opposite direction. The current is induced only when there is a changing magnetic field.
Now let us try it with a soft-iron core through coil A and coil B. Insert soft iron rod in coils A and B. Is the induced current larger now? Observe the deflection of needle of the galvanometer connected to the coil B. It is observed that the deflection is larger than before. The larger deflection of needle indicates that the induced current in coil B is more.Fleming’s right hand rule is used to find the direction of induced current. It states that on stretching the thumb, forefinger and middle finger of the right hand such that fore finger indicates the direction of magnetic field, and them shows the direction of motion of conductor then the middle finger will indicate the direction of induced current.
