Question

A parallel-plate capacitor has a capacitance of 2.1 µF with air between the plates. The capacitor is connected to a 24 V battery and charged. The battery is then removed. When a dielectric is placed between the plates, a potential difference of 2.8 V is measured across the plates. What is the dielectric constant of the material?

Answer 1

In an isolated instance the voltage goes down by a factor of K.

24 v / k = 2.8 v
k = 8.6 (rounded to sig figs)