The refractive index of water with respect to vacuum is 
and refractive index of vacuum with respect to glass is 
. If the speed the speed of light in glass is 2 × 108 ms-1, find the speed of light in (i) vacuum, (ii) water.
Given;
Refractive index of (R.I) water w.r.t vacuum
;
Refractive index (R.I) of vacuum w.r.t glass 
;
Refractive index (R.I) of glass to vacuum will be = 
Refractive index of glass to water = 
⇒ Refractive index of glass w.r.t water = 
⇒ 
⇒ 
⇒ speed of light in water
⇒ speed of light in water
Thus, speed of light in water = 2.25 × 108.
Refractive index of water w.r.t vacuum = vμw 
;
⇒ 
⇒ 
⇒ 
Thus, speed of light in vacuum is 3 × 108 m/s.
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