Short answerEasy1 mark
Refractive index of glass with respect to water is 9/8. Find the refractive index of water with respect to glass.
Topic: Relative refractive index
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Answer
Exam answer
Given: refractive index of glass with respect to water, _wμ_g = 9/8
Reversing the two media gives the reciprocal: _gμ_w = 1 ÷ (_wμ_g)
_gμ_w = 1 ÷ (9/8) = 8/9
Refractive index of water with respect to glass = 8/9
Explanation
Swap the order of the two media and the refractive index turns upside down. Nothing else is needed.
Read the subscripts as "of X with respect to Y" — that is the whole question. Glass with respect to water is 9/8 (greater than 1, because glass is the denser of the two); water with respect to glass is 8/9 (less than 1, as it must be when going from denser to rarer).
Use that as a check: whenever the first medium named is the RARER one, the answer must come out below 1.
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