Capacitance before introduce dielectric Cb
Cb=10×10−6F
Q=CbV=10−5×20=2×10−4C
Capacitor after introduce dielectric Ca
Ca=kCb=4×10×10−6F=4×10−5F
Q=CaV=4×10−5×20=8×10−4F
(a) charge before the
dielectric was introduced. Q=2×10−4C
(b) charge After the dielectric was introduced,
Q=4×10−4C