MHT CET · Physics · Capacitance

Three parallel plate air capacitors are connected in parallel. Each capacitor has plate area $\frac{A}{3}$ and the separation between the plates is $d, 2 d$ and $3 d$ respectively. The equivalent capacity of combination is ( $\varepsilon_0=$ absolute permittivity of free space)

A $\frac{7 ε_{0} A}{18 d}$
B $\frac{11 ε_{0} A}{18 d}$
C $\frac{13 ε_{0} A}{18 d}$
D $\frac{17 ε_{0} A}{18 d}$

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Answer & Solution

Correct Answer

(B) $\frac{11 ε_{0} A}{18 d}$

Step-by-step Solution

Detailed explanation

C = Q V a n d C = \frac{ε_{0} A}{d}

As given

C_{1} = \frac{ε_{0} . A}{3 d};

C_{2} = \frac{ε_{0} A}{6 d};

C_{3} = \frac{ε_{0} A}{9 d}

∴ C e q = C_{1} + C_{2} + C_{3} for

parallel combination of capacitors

∴ C_{e q} = \frac{ε_{0} A}{d} (\frac{1}{3} + \frac{1}{6} + \frac{1}{9}) = \frac{11 ε_{0} A}{18 d}

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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Three parallel plate air capacitors are connected in parallel. Each capacitor has plate area \(\frac{A}{3}\) and the separation between the plates is \(d, 2 d\) and \(3 d\) respectively. The equivalent capacity of combination is ( \(\varepsilon_0=\) absolute permittivity of free space)

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