Self - Induction

Electromagnetic Induction of Class 12


Electromagnetic induction appears in all cases when the magnetic flux through a loop changes. It is not important at all what causes the variation of the flux. If in a certain loop there is a time varying current the magnetic field of the current will also change and this leads to the variation of the magnetic flux through the loop, and hence to the appearance of induced emf.

Thus, the variation of current in a circuit leads to the appearance of an induced emf in this circuit. This phenomenon is called self-induction.

Self - Induction

Let us consider a coil in series with a switch and a battery as shown in Fig. 4.17 (a) when the switch is first closed, the growing current creates a changing magnetic field. As the flux through the coil changes, there is an induced emf that opposes this change. 

It tries to prevent the rise in the current. As a result, the current does not reach its final value instantly, but instead rises gradually as shown in Fig 4.17 (b). When the switch is opened, the flux rapidly decreases.  This time the self induced emf tries to maintain the flux, it has the same polarity as the battery.

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