<Dl> <Dd> U E S = 1 2 ε ∫ V E 2 d V, (\ displaystyle U_ (ES) = (\ frac (1) (2)) \ varepsilon \ int _ (V) \ mathbf (E) ^ (2) \, \ mathrm (d) V \,,) </Dd> </Dl> <Dd> U E S = 1 2 ε ∫ V E 2 d V, (\ displaystyle U_ (ES) = (\ frac (1) (2)) \ varepsilon \ int _ (V) \ mathbf (E) ^ (2) \, \ mathrm (d) V \,,) </Dd> <P> In the presence of matter, it is helpful to extend the notion of the electric field into three vector fields: </P> <Dl> <Dd> D = ε 0 E + P (\ displaystyle \ mathbf (D) = \ varepsilon _ (0) \ mathbf (E) + \ mathbf (P) \!) </Dd> </Dl>

What is the formula for electric field strength