A capacitor stores 10mC charge when connected across a battery. When the gap between the plates is filled with a dielectric, a charge of 20mC flows through the battery. Find the dielectric constant of the dielectric.

k = 3

In absence of dielectric Q = CV = 10μC

With dielectric , A charge of $20 \mu C$ flw from the battery hence total charge becomes $30\mu C$

 $\Rightarrow Q'= kCV = 30\mu C$

$ k = \frac{Q'}{Q} = 3$