Refractive index of medium 1 w.r.t. medium 2 is n₁₂. Then:
An₁₂ = n₁/n₂
Bn₁₂ × n₂₁ = 1 (reciprocal)
Cn₁₂ = n₁ + n₂
Dn₁₂ + n₂₁ = 0
Answer & Solution
Correct answer: B. n₁₂ × n₂₁ = 1 (reciprocal)
n₁₂ × n₂₁ = 1 (always). Hence n₁₂ = 1/n₂₁. Also n₁₂ = v₂/v₁ (ratio of speeds). The 'absolute' refractive index uses medium = vacuum/air.
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