Question

An EM wave from air enters a medium. The electric fields are ${\stackrel{→}{E}}_1=E_{01}\hat{x}\cos \left[2\mathrm{π}\mathrm{ν}\left(\frac{z}{c}-t\right)\right]$ in air and ${\stackrel{→}{E}}_1=E_{01}\hat{x}\cos \left[k\left(2z-ct\right)\right]$ in medium, where the wave number k and frequency v refer to their values in air. The medium is non-magnetic. If ${∈}_{r_1}and {∈}_{r_2}$ refer to relative permittivity of air and medium respectively, which of the following options is correct ?