Question

A parallel plate capacitor of capacitance $90pF$ is connected to a battery of emf $20V$. 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. $2.4nC$
• B. $0.9nC$
• C. $1.2nC$
• D. $0.3nC$

Answer 1

The correct option is C $1.2nC$

$Q_{cap}={KC}_{0}V$
$\left|Q_{\text{polarised}}\right|=\left|Q_{\mathrm{cap}}(1-\frac{1}{k})\right|$
$=(90\times {10}^{-12})\left(20\right)\left(\frac{5}{3}\right)(1-\frac{3}{5})$ coulombs
$=1200\times {10}^{-12}$ coulombs
$=1.2nC$