The speed of any electromagnetic wave (EM) like light in any medium of permeability, μ and permittivity, ε is given by v=με1 Also, μ=μ0μr and ε=ε0εr where, μ0 and ε0 are permeability and permittivity in free space and μr and εr are relative permeability and relative permittivity of medium respectively. Here, μr=1.0 εr=1.44 ∴v=μrεrμ0ε01=μrεrc[∵c=μ0ε01]=1×1.443×108=2.5×108 ms−1