Capacitance of air capacitor
C0=ε0Ad=3μF ......... (i)
When a dielectric of permittivity εr and dielectric constant K is introduced between the plates, then
Capacitance, C=Kε0Ad=15μF ..... (ii)
Dividing eq. (ii) by (i), we get
CC0=KϵoAdε0Ad=153
⇒K=5
∴ permittivity of the medium
ε0=ε0K
=8.85×10−12×5=0.44×10−10