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The area of every plate shown in the figure is A and the separation between successive plates is d. What is the capacitance between points a and b?

Asked in GSEB Board July 2017 · Capacitor networks

Figure: Capacitor networks
Answer: (2) (2ε₀A)/d

Step-by-step solution

Given: three identical plates of area A, successive gaps d; the two outer plates are joined to a and the middle plate to b (see figure).

Idea: each gap between a plate at a and a plate at b is a parallel-plate capacitor C₀=(ε₀A)/d.

The upper gap lies between an a-plate and the b-plate: one capacitor C₀.

The lower gap does the same: a second capacitor C₀.

Both sit between the same two points a and b, so they are in parallel: C=C₀+C₀=(2ε₀A)/d.

Why the other options are wrong

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