What is self induction ? Obtain expression for self induced emf.

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→When electric current through an isolated conducting coil is changed, magnetic flux linked with it changes. As a result, induced emf is produced in the coil. This phenomenon is called self induction.
→Here, induced emf is called self induced emf.
→Suppose, electric current passing through an isolated coil having N turns is I .
→Total magnetic flux linked with coil,
$\begin{array}{c}
N \phi_{ B } \propto I \\
\therefore \quad N \phi_{ B }= L I
\end{array}$
→Proportionality constant L in equation (1) is called self inductance.
→On changing current with time, magnetic flux linked changes. As a result, induced emf is produced.
$\therefore N \frac{d \phi_{ B }}{d t}= L \frac{d I }{d t}$
→According to Faraday's law,
$\varepsilon=- N \frac{d \phi_{ B }}{d t}$
From equation (2) and (3),
$\varepsilon=- L \frac{d I }{d t}$
Equation (4) is expression for self induced emf.

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