A plane electromagnetic wave propagating in a non-magnetic dielectric medium is given by  E=E0sin[4×10−7x−50t].Where 'x' is in meter and 't' is in second. If the relative permeability of the medium, μr=1 then the dielectric constant of the medium is

Speed of electromagnetic wave in Vacuum is  C=1μ0∈0Speed of electromagnetic wave in a dielectric medium of dielectric constant (k) is given by  C'=1kμ0∈0=CkFrom given equation  C'=angular velocitywave number=504×10−7=54×108m/sAnd C=3×108m/s Using, C'=Ck⇒54×108=3×108k                       ⇒ 2516=9k ⇒k=9×1625=5.76