Define self-inductance of a coil. Obtain the expression for the energy stored in an inductor L connected across a source of emf.

Explanation

### Step-by-Step Solution:

**Step 1: Define Self-Inductance**
Self-inductance (L) of a coil is defined as the property of the coil that induces an electromotive force (EMF) in itself due to a change in current flowing through it. This induced EMF opposes the change in current according to Lenz's law. Mathematically, it is expressed as:
\[ \epsilon = -L \frac{di}{dt} \]
where \( \epsilon \) is the induced EMF, \( L \) is the self-inductance, and \( \frac{di}{dt} \) is the rate of change of current.

**Step 2: Consider an Inductor Connected to a Source of EMF**
...