Energy Stored by Capacitor Video Lessons

Concept

# Problem: Part A. Find the energy U0 stored in the capacitor. Express your answer in terms of A, d, V, and ϵ0.Part B. The capacitor is now disconnected from the battery, and the plates of the capacitor are then slowly pulled apart until the separation reaches 3d. Find the new energy U1 of the capacitor after this process.Express your answer in terms of A, d, V, and ϵ0.Part C. The capacitor is now reconnected to the battery, and the plate separation is restored to d. A dielectric plate is slowly moved into the capacitor until the entire space between the plates is filled. Find the energy U2 of the dielectric-filled capacitor. The capacitor remains connected to the battery. The dielectric constant is K.Express your answer in terms of A, d, V, K, and ϵ0.

###### FREE Expert Solution

Energy stored in a capacitor,

$\overline{){\mathbf{U}}{\mathbf{=}}\frac{\mathbf{1}}{\mathbf{2}}{\mathbf{C}}{{\mathbf{V}}}^{{\mathbf{2}}}}$

The capacitance of a parallel plate capacitor,

$\overline{){\mathbf{C}}{\mathbf{=}}\frac{{\mathbf{\epsilon }}_{\mathbf{0}}\mathbf{A}}{\mathbf{d}}}$

Part A

Substitute the capacitance in the Energy equation,

${{\mathbit{U}}}_{{\mathbf{0}}}{\mathbf{=}}\frac{\mathbf{1}}{\mathbf{2}}{\mathbf{\left(}}\frac{{\mathbit{\epsilon }}_{\mathbf{0}}\mathbit{A}}{\mathbit{d}}{\mathbf{\right)}}{{\mathbit{V}}}^{{\mathbf{2}}}$

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###### Problem Details

Part A. Find the energy U0 stored in the capacitor. Express your answer in terms of A, d, V, and ϵ0.

Part B. The capacitor is now disconnected from the battery, and the plates of the capacitor are then slowly pulled apart until the separation reaches 3d. Find the new energy U1 of the capacitor after this process.

Part C. The capacitor is now reconnected to the battery, and the plate separation is restored to d. A dielectric plate is slowly moved into the capacitor until the entire space between the plates is filled. Find the energy U2 of the dielectric-filled capacitor. The capacitor remains connected to the battery. The dielectric constant is K.

Express your answer in terms of A, d, V, K, and ϵ0.