An EM wave from air enters a medium. The electric fields are $\overrightarrow {{E_1}}$=$${E_{01}}\widehat x\cos \left[ {2\pi v\left( {{z \over c} - t} \right)} \right]$$ in air and $\overrightarrow {{E_2}}$ =$${E_{02}}\widehat x\cos \left[ {k\left( {2z - ct} \right)} \right]$$ in medium, where the wave number k and frequency $u$ refer to their values in air. The medium is non-magnetic. If ${\varepsilon _{{r_1}}}$ and ${\varepsilon _{{r_2}}}$ refer to relative permittivities of air and medium respectively, which of the following options is correct ?