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Physics

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PHS 5041 Optics Refraction of Light

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Refraction always occurs simultaneously with some partial reflection Change in direction is with respect to the normal (different angle of incidence and refraction) Perpendicular rays DO NOT refract (reflection only)

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PHS 5041 Optics Refraction of Light Laws of Refraction: _Incident ray, refracted ray and the normal lie on the same plane _ n 1 sinθ 1 = n 2 sinθ 2 (Snell’s Law) n 1 : index of refraction of medium 1 n 2 : index of refraction of medium 2 θ 1 : angle of incidence θ 2 : angle of refraction

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PHS 5041 Optics Refraction of Light Index of refraction is a measurement of a medium’s optical density

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PHS 5041 Optics Refraction of Light Example: A light ray passes from air into a liquid. If incident angle is 40° and refraction angle is 28.2°. Identify the liquid. n 1 sinθ 1 = n 2 sinθ 2 n 2 = n 1 sinθ 1 / sinθ 2 n 2 = (1.003)(sin 40°) / (sin 28.2°) n 2 = 1.36 (Ethyl alcohol)

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PHS 5041 Optics Refraction of Light Perpendicular incident rays DO NOT refract (reflection only)

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PHS 5041 Optics Refraction of Light When light goes from a less optically dense medium to a more optically dense medium (n 1 < n 2 ), it bends TOWARD the normal

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PHS 5041 Optics Refraction of Light When light goes from a more optically dense medium to a less optically dense medium (n 1 > n 2 ), it bends AWAY from the normal

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PHS 5041 Optics Refraction of Light Critical angle: Incident angle for which the refracted angle is 90 degrees sin θ c = n 2 / n 1 or sin θ c = sin θ 1 / sin θ 2 (n 1 must be higher than n 2 )

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PHS 5041 Optics Refraction of Light Total Internal Reflection: Occurs when the incident angle is HIGHER than the critical angle ONLY occurs when light travels from a more to a less optically dense medium

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PHS 5041 Optics Refraction of Light Example: An angle of refraction of 74.6° in air corresponds to an angle of incidence of 40° in crown glass. Which of these two media can produce total internal reflection? Why? Find the value of the critical angle. _Crown glass is the one that produces TIR for it is more optically dense than air (n g > n a ). Also incident angle < refracted angle sin θ c = sin θ 1 / sin θ 2 sin θ c = sin 40° / sin 74.6° sin θ c = 0.6667 θ c = 41.8°

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PHS 5041 Optics Refraction of Light Light velocity is affected as light travels from vacuum into another medium: n x = c / v x n x : index of refraction of medium x v x : velocity of light in medium x c : velocity of light in vacuum (3 * 10 8 m/s)

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PHS 5041 Optics Refraction of Light Example: Calculate the index of refraction of Plexiglas knowing that the speed of light in this material is 1.99 * 10 8 m/s. n p = c / v p n p = (3 * 10 8 m/s) / (1.99 * 10 8 m/s) n p = 1.51

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PHS 5041 Optics Refraction of Light

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Applications:

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PHS 5041 Optics Refraction of Light Applications:

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PHS 5041 Optics Refraction of Light Applications:

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PHS 5041 Optics Refraction of Light Applications:

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PHS 5041 Optics Refraction of Light Applications:

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