Physics Electrostatic Potential and Capacitance

Two isolated conducting spheres S₁ and S₂ of radius (2/3)R and (1/3)R have 12µC and -3 µC charges, respectively, and are at a large distance from each other. They are now connected by a conducting wire. A long time after this is done the charges on S₁ and S₂ are respectively:

In the circuit shown in the figure, the total charge is 750 µC and the voltage across capacitor C? is 20 V. Then the charge on capacitor C? is

A 5µF capacitor is charged fully by a 220 V supply. It is then disconnected from the supply and is connected in series to another uncharged 2.5µF capacitor. If the energy change during the charge redistribution is X/100 J then value of X to the nearest integer is:

A parallel plate capacitor has plate of length ' $$ l', width ' w$$ ' and separation of plates is 'd $$ '. It is connected to a battery of emf V$$ . A dielectric slap of the same thickness 'd $$ ' and of dielectric constant $$ k = 4 is being, inserted between the plates of the capacitor. At what length of the slab inside plates, will be energy stored in the capacitor be two times the initial energy stored?