Calculating the Energy Stored in the Field of a Solenoid

The energy is given by the equation $E_{\text{ind}}=\frac{1}{2}{\text{LI}}^2$, and all quantities except $E_{\text{ind}}$ are known.

Substituting the value for $L$ found in the previous example and the given current into $E_{\text{ind}}=\frac{1}{2}{\text{LI}}^2$ gives

This amount of energy is certainly enough to cause a spark if the current is suddenly switched off. It cannot be built up instantaneously unless the power input is infinite.