If the electric field between the plates of a capacitor is 400 V/m, what will be the energy density of the field?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → 0.7 μJ/m3
The energy density of an electric field depends only on the field strength.
\( \displaystyle u = \frac{1}{2}\varepsilon_0 E^{2} \)
\( \displaystyle u = \frac{1}{2} \times 8.85\times10^{-12} \times (400)^{2} \)
\( \displaystyle u = 0.5 \times 8.85\times10^{-12} \times 1.6\times10^{5} \)
\( \displaystyle u \approx 7.1\times10^{-7}\,\mathrm{J\,m^{-3}} \)
\( \displaystyle u \approx 0.7\,\mu\mathrm{J\,m^{-3}} \)