The capacity of a condenser increases both, when a conducting slab or an insulating slab is introduced between the plates of the condenser. In the former case, electric field `E = 0` inside the conductor and in the latter case, `E lt E_(0)`, inside the insulator. Thus, potentai difference `V = E xx d` decreases and hence capacity `C = Q//V` increases. It should be clearly understood that when a dielectric slab is introduced inbetween the plates of a charged capacitor with battery connected across the plates, (i) Capacity `C` increases, (ii) Potential `V` remains constant, (iii) Charge `Q = CV`, increases, (iv) Electric field `E` decreases, (v) Energy stored `U = (1)/(2) CV^(2)` increases. However, when battery across the plates of charged capacitor is put off and dielectric slab is introduced inbetween th plates of the capacitor, (i) Capacity `C` increases, (ii) charge `Q` remains constant, (iii) Potential `V = (Q)/(C )` decreases, (iv) Electric field. `E = V xx d` decreases, (v) Energy stored `U = (Q^(2))/(2C)` decreases. Consider a parallel plate air capacitor with area of each plate `= 150 cm^(2)` and distance between its plates `= 0.8mm`. With the help of the passage given above, choose the most appropriate for each of the following questions : What will be the potential of the capacitor when filled with dielectric after charging as air capacitor ?A. `1200 V`B. `400 V`C. `3600 V`D. `300 V`