Question

A parallel plate capacitor of capacitance 90 pF is connected to a battery of emf 20V. If a dielectric material of dielectric constant K = 5/3 is inserted between the plates, the magnitude of the induced charge will be :-
(1) 0.3 n C

(2) 2.4 n C

(3) 0.9 n C

(4) 1.2 n C

Answer 1

Ans. (4)

Q = (kC) V
=(5/3*90 pF) (20V) = 3000 pC= 3 nC
induced charges on dielectric Q_ind = Q(1-1/k)= 3 nC(1-3/5) =1.2nC