Question

A paralle plate capacitor having capacitance $12\text{pF}$ is charged by a battery to a potential difference of $10\text{V}$ between its plates. The charging battery is now disconnected and a porcelain slab of dielectric constant $6.5$ is slipped between the plates. The work done by the capacitor on the slab is

• A. $692\text{pJ}$
• B. $508\text{pJ}$
• C. $560\text{pJ}$
• D. $600\text{pJ}$

Answer 1

The correct option is B $508\text{pJ}$

Work done by capacitor on the slab can be written as
$W=-\Delta U$
$W=(-1)|\frac{(CV{)}^2}{2KC}-\frac{(CV{)}^2}{2C}|$
$W=\frac{(CV{)}^2}{2C}\frac{K-1}{K}$
$W=508\text{J}$.