In a medium the speed of light decreases to 0.2 times its speed in free space. The ratio of relative permittivity to refractive index of the medium is x : 1. The value of x i s ______. [For the medium μ(r)=1]

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G1 Physics · Accepted Answer

Refractive index n = c/v = 1/0.2 = 5. For μ(r)=1, n² = ε(r), so ε(r)=25. Therefore ε(r)/n = 25/5 = 5, hence x=5.