Question

A radio capacitor of variable capacitance is made of n parallel plates each of area A and separated from each other by a distance d.The alternate plates are connected together.The capacitance of the combination is

Answer 1

if n capacitors connected in series then
1/c= 1/c1+1/c2+.........1/cn
we know capacitance =
epsilon(3) x area /distance

then 1/c= d/3A (1+2+3.....+n)
sum of n terms equals to n(n+1)/2
therefore c =3A.n(n+1) /2d
is the required capacitance