# Physics. PHS 5041 Optics Refraction of Light Refraction always occurs simultaneously with some partial reflection Change in direction is with respect.

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Physics

PHS 5041 Optics Refraction of Light

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)

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

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

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)

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

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

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

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 )

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

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°

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)

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

PHS 5041 Optics Refraction of Light

Applications:

PHS 5041 Optics Refraction of Light Applications:

PHS 5041 Optics Refraction of Light Applications:

PHS 5041 Optics Refraction of Light Applications:

PHS 5041 Optics Refraction of Light Applications:

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