Question

A plate capacitor C has an initial charge Q and plates separation d. A dielectric material (k=2) is inserted between the plates at the mean while the separation parallel between the plates is doubled (to become 2d). So, in this process one statement below is wrong:

a) U is the same

b) Q is the same

c) V is the same

d) E is the same

Answer 1

Paralle plate capacitor

   capacitance         A effective area between the plates of a capacitor
                       d is separation of the plates

   C is propotional to A and inversly proportional to d

if dielectric material inserted then capacitance C2 = k C1             C1 is capacitance without dielectric material

                       C2 = k epsilon not A/2d

                       C1/C2 = d2/ kd1
                      
                       C1/C2 = 2d1/2*d1
                       C1/C2 = 1
capacitance remains same so energy U = 1/2 CV^2 , potential also same but electric field changes when a dielctric material placed

Ans D