Electrical Engineering ⇒ Topic : Energy Density of Electric Field

Energy Density of Electric Field

The energy stored per unit volume of the electric field is called energy density of the electric field

   We have seen that energy is stored in the electric field of a capacitor. In fact,wherever electric field exists, there is stored energy. While dealing with electric fields, we are generally interested in energy density (u) i. e. energy stored per unit volume. Consider a charged parallel plate capacitor of plate area A and plate separation d as shown in Fig.(a).

                                                                     figure (a)

We know that capacitance of a parallel plate capacitor is C = ε₀A/d.

But V/d is the electric field intensity (E) between the plates.

Obviously, the unit of energy density will be joules/m³.

Therefore, energy density (i.e., electric field energy stored per unit volume) in any region of space is directly proportional to the square of the electric field intensity in that region.

Note that we derived exps. (i) and (i i) for the special case of a parallel plate capacitor. But it can be shown to be true for any region of space where electric field exists.

Note. We can also express energy density of electric field in terms of electric flux density D = (ε₀ε_r E)