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 is ______. [For the medium μ(r)=1]
Physics · Circular Motion
JEE Mains 31 January 2023 Shift 1 Morning Shift

Question

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 is ______. [For the medium μ(r)=1]

Physics · Circular Motion

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.