Find out equivalent capacitance between A and B.

Explanation

Let `C=(Ain_(0))/(d)` Equivalent circuit :
`(1)/(C_(eq))=(1)/(C)+(2)/(3C)=(5)/(3C)`
`C_(eq)=(3C)/(5)=(3Ain_(0))/(5d)`
Alternative Method : Let charge distribustion on plates as shown :
`C=(Q)/(V)=(x+y)/(V_(AB))`
Potential of 1 and 4 is same
`(y)/(A in_(0))=(2x)/(A in_(0)) " " y=2x`
`V=((2y+x)/(A epsilon_(0))) d rArr C=((x+2x)A in_(0))/((5x)d)=(3A in_(0))/(5d)`.