Question

if a dielectric slab is introduced between a parallel plate capacitor with the battery connected, then how do the following quantities change?
1 charge
2 potential
3 capacitance
4 energy

Answer 1

The battery maintains a constant voltage across the plates. The dielectric increases the capacitance so the battery must increase the charge Q on the plates to keep V constant.
[Suppose K is the dielectric constant, then
C'=KC
Capacitance increases.
Since the battery is connected, potential difference will remain unchanged.
Also the charge on capacitor will increase as capacitor can draw more charge from the battery.
Since potential difference between plates does not change, electric filed will also remain unchanged but the energy stored will increase.]