A4kash:
I understood that part...but similarly
"The induced voltage creates a current in the coil that flows either with or against the main coil current,depending on whether the coil current is incresing or decresing.if the coil current is incresing,the additional current flows against the main coil current but when the coil current is decresing, the additional current flows with the main coil current"
and my qsn is why does it happen so?why the additional current flows against when the main coil current when the coil current is increasing and similarly flows with the main coil current if the coil current is decrasing??
Erm, that text is pretty poorly phrased/misleading.
The total EMF in the circuit, combined with the various elements of the circuit (resistances, whatever) determine the current. But
the total EMF includes the induced EMF which itself is determined by the rate-of-change of current. Thus there is a circular
interdependence between current and voltage in the circuit.
You typically have to solve a differential equation to predict the result evolving in time...
Energy is conserved in an inductor so you won't see an increase in current causing an increase in current (ad infinitem)...
If the magnitude of the current is increasing then energy is flowing into the magnetic field, so is being taken from
the rest of the circuit, which is why the back EMF (as its called) always seems to oppose the change in current
(the external circuit has to work harder to pump energy into the magnetic field if the field is increasing).
When the field is decreasing the EMF will seem to want to preserve the field (actually it is the means that energy is put back into
the circuit from the field.) Attempting to stop the current in an inductor very quickly will induce a very large EMF (which
allows the field energy to force its way back into the circuit quickly). Thus a low voltage circuit containing an inductor
can generate upto thousands of volts (limited mainly by the switching device used to arrest current flow).