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Q.
Four identical plates each of area a are separated by a distance $d$. The connection is shown below. What is the capacitance between $P$ and $Q$ ?
WBJEEWBJEE 2013Electrostatic Potential and Capacitance
Solution:
Suppose the pair of plates is connected to positive terminal of the battery and the pair of
plates Q is connected to the negative terminal of the battery.
From figure, it is clear that we have two capacitors $C_{1}$ and $C_{2}$. Positive plates of $C_{4}$ are connected to positive plate of $C_{2}$ and negative plate to negative. Therefore $C_{1}$ and $C_{2}$ are in parallel.
So, $C_{p}=C_{1}+C_{2}=2 C=\frac{2 \varepsilon_{0} a}{d}$
