A red colour light of wavelength 760nm is observed to pass from air to an unknown medium. If the wavelength of light in unknown medium becomes 570nm, the unknown medium is
A
optical denser
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B
optical rarer
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C
same as initial medium
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D
Data insufficient
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Solution
The correct option is A optical denser Refractive index, μ=λvaccumλmedium ⇒μ∝1λ ∵λ1=760nm,λ2=570nm ⇒λ1>λ2
or, μ2>μ1
Thus, unknown medium is optical denser.
Tips: Relate Snell's law with the wave properties (v,λ) of light.