The motion of the magnet in either direction causes a change in strength of the magnetic field linked with the coil and this causes a current to be induced in the coil. This induced current opposes the change in the magnetic field by producing its own magnetic field.
Whenever an EMF is induced, the induced current is in such a direction so as to oppose the change inducing the current.
The negative sign indicates the opposing nature of the induced EMF.
(i) Changing the magnitude of magnetic field B
