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The electrostatic force between the metal plates of an isolated parallel plate capacitor C having a charge Q and area A, is

Asked in NEET 2018 · Force between capacitor plates

• (1) independent of the distance between the plates
• (2) linearly proportional to the distance between the plates
• (3) proportional to the square root of the distance between the plates
• (4) inversely proportional to the distance between the plates.

Step-by-step solution

Why the other options are wrong

• (2) Takes the stored energy U=(Q²d)/(2ε₀A), which does grow with d, for the force; the force is the rate at which U changes with separation, (Q²)/(2ε₀A), which does not depend on d.
• (3) No relation between these quantities brings in √d; the force depends only on Q and A.
• (4) Writes F=QV/d and holds V fixed; for an isolated capacitor Q is fixed and V itself grows in proportion to d.

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