Question

A ray of light enter a rectungular glass slab of refractive index 1.5 .If its speed in air is 3×10^8 m/sec then what is the spped in glass?

Answer 1

refractive index of a medium μ
         = speed of light in vacuum / speed of light in the medium
         =  c / v
      v  = c / μ
         = 3 * 10^8 / 1.5 =  2 * 10^8 m/sec

Answer 2

refractive index= speed of light in air/speed of light in a medium                                    ie 1.5=3 x10^8/speed in glass  then speed in glass=3x10^8/1.5 =30x10^8/15 = 2x10^8m/sec