The plates of parallel plate capacitor are charged upto 100 V. A 2 mm thick plate is inserted between the plates. Then to maintain the same potential difference, the distance between the plates is increased by 1.6 mm. The dielectric constant of the plate is

In air the potential difference between the plates Vair =σε0⋅d                  …(i)In the presence of partially filled medium potential difference between the plates Vm=σε0(d−t+tK)            …(ii)Potential difference between the plates with dielectric medium and increased distance is Vm'=σε0(d+d')−t+tK            …(iii)According to question Vair=Vm' which gives K=tt−d'Hence K=22−1.6=5