Consider a layer of Oil, Glass, and Air where the oil/glass boundary is parallel to the glass/air boundary. Let the inde

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Consider a layer of Oil, Glass, and Air where the oil/glass
boundary is parallel to the glass/air boundary. Let the index of
refraction for the glass be 1.57 and the index of refraction for
the oil to be 1.4. At what angle relative to the normal should a
ray of light be directed upon the oil/glass interface such that it
strikes the glass/air interface at the critical angle?
Oil __________________________________________________
Glass _________________________________________________
Air