Work of forces of the electric field when moving the charge q between two points of equal field qU, if the voltage U remains constant. However, when charging the capacitor the voltage across its plates rises from zero to U, and when evaluating the work of the field in this case the voltage of you need to take its average value. Thus,

A = qU_MS = q(U+0)/2 = qU/2.

Since this work is on the increase in energy W_E charged capacitor, we W_E=And. Therefore, the energy of the charged capacitor is expressed by the formula:

W_E=qU/2. (15.24)

Since q=CU, we get another formula for the energy of the capacitor:

W_E=CU²/2. (15.24and)

These formulas allow us to calculate the energy of a charged conductor relative to the Earth. The voltage in this case can be found by checking the electrometer.

Here the question arises: is energy W_E energy charges on the capacitor plates or the energy field, created these charges? According to the theory of close-range interaction with this energy field has. Since the condenser field is concentrated in the space between its plates and uniformly, the energy of this field is uniformly distributed in this space.

Volumetric energy density ω of a uniform electric field is value, which is measured by energy fields, enclosed in a unit volume:

ω_E= W_E/V. (15.25)

Replacing With in (15.24and) the value of (15.20), get

W_E= CU²/2=ε_WithSU²/2d.

Multiplying the numerator and denominator of the right side on d, will have

W_E=ε_With/2* U²/d²Sd

As Sd=V, and E=U/d, get W_E=(ε_WithE²/2)*V, where

ω_E= W_E/V= ε_WithE²/2 (15.26)

The energy density of the electric field is directly proportional to the square of the strength of this field.