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Question:

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

Proportional to the square root of the distance between the plates

Linearly proportional to the distance between the plates

Independent of the distance between the plates

Inversely proportional to the distance between the plates

Solution:

Since Electric field due to one plate of capacitor is given as E = σ/2ε₀ E = Q/2Aε₀
Now force on another plate due to first plate will be given by F = QE
F = Q²/2Aε₀
Hence, it is independent of distance between plates.