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If the distance between two parallel plates of a capacitor is \(d\), \(A\) is the area of each plate, and \(E\) is the e…

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If the distance between two parallel plates of a capacitor is \(d\), \(A\) is the area of each plate, and \(E\) is the electric field, find the energy stored in the capacitor.

(Shift I - Memory Based)

a

\(\frac{1}{2}{E}^{2}A{ϵ}_{0}d\)

b

\(\frac{1}{4}{E}^{2}A{ϵ}_{0}d\)

c

\(\frac{3}{4}{E}^{2}A{ϵ}_{0}d\)

d

\({E}^{2}A{ϵ}_{0}d\)

✓ Correct answer: a)

\(\frac{1}{2}{E}^{2}A{ϵ}_{0}d\)

Explanation
  • The capacitance of the parallel plate capacitor is: \(C={ϵ}_{0}\frac{A}{d}\mathrm{.}\)
  • Energy stored in a capacitor: \(U=\frac{1}{2}C{V}^{2}\mathrm{.}\)
  • Substituting \(V=Ed\) and \(C={ϵ}_{0}\frac{A}{d}\)​:
  • \(U=\frac{1}{2}{ϵ}_{0}\frac{A}{d}(Ed{)}^{2}=\frac{1}{2}{E}^{2}A{ϵ}_{0}d\mathrm{.}\)

Thus, the energy stored is \(\frac{1}{2}{E}^{2}A{ϵ}_{0}d\)

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