Question

A parallel plate capacitor of capacitance $90\, pF$ is connected to a battery of emf $20\, V$. If a dielectric material of dielectric constant $K = \frac{5}{3}$ is inserted between the plates, the magnitude of the induced charge will be :

• A. 1.2 n C
• B. 0.3 n C
• C. 2.4 n C
• D. 0.9 n C

Answer 1

Answer: (A)

1.2 n C

Answer 2

$C'=K C_{0}$
$Q=K C_{0} V$
$Q_{\text {induced }}=Q\left(1-\frac{1}{K}\right)$
$=\frac{5}{3} \times 90 \times 10^{-12} \times 20\left(1-\frac{3}{5}\right)$
$=1.2\, nC$