Plate $A$ of a parallel plate air filled capacitor is connected to a spring having force constant  $\text{'}K$ and plate $B$ is fixed. They rest on a frictionless table top as shown in figure. If $+q$ and $-q$ charges are given to $A$ and $B$ very slowly then elongation in spring will be

Find $C_{eq}$ of the following (Equivalent capacitance between).

(i)  (ii) 

(iii)  (iv) 

Area of each plate $=A.$ Find $C_{AB}$ (equivalent).

(i) Find equivalent capacitance between $A$ and $B.$
(ii) Find potential differences between $A_1$ and $B_1.$

Find work by battery after the switch is closed, if initial charge were zero on all the capacitors.

Five plates (same plate area for each) are placed as shown in figure. The separation between any two consecutive plates is $d.$ Then find $C_{AB}.$

Find charge on three capacitors.

In the given figure, potentials of points $A$ and $B$ are