# The absolute refractive indices of glass and water are 4/3 and 3/2 respectively. If the speed of light in glass is 2 × 108 m/s, calculate the speed of light in (i) vacuum, (ii) water.

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Absolute refractive index of glass is, μg=32 Speed of light in glass, vg = 2 × 108 m s−1 According to Snell's law μg=cvg⇒c = μgvg⇒c=32×2×108 ⇒c=3×108 m s-1 Hence, the speed of light in vacuum is 3 × 108 m s−1. (ii) Let the speed of light in water be vw Absolute refractive index of water, μw=43 Speed of light in vacuum, c = 3 × 108 m s−1 μw=cv⇒vw=cμw⇒vw=3×10843⇒vw=9×1084 ⇒vw=2.25×108 m s-1 Hence, the speed of light in glass is 2.25 × 108 m s−1 Disclaimer: In the given question, the refractive indices of glass and water are wrong.

The question is solved according to correct values, that is the values of refractive indices of water and glass are taken to be 4/3 and 3/2, respectively.