Refraction of light
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Refraction is the change in direction of light when it passes from one medium to another. Light bends towards the normal when traveling from a less dense to a more dense medium, and away from the normal in the opposite case. The ratio of sines of the angle of incidence and refraction is a constant called the refractive index, which depends on the optical densities of the media. Total internal reflection occurs when light travels from a denser to a less dense medium at an angle greater than the critical angle.
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Refraction of light
- 2. LIGHT Refraction is the change in direction of light when it passes from one medium to another.
- 3. LIGHT If light ray enters another medium perpendicular to boundary, the ray does not bend.
- 4. LIGHT When the light ray travels from air to water, the refracted ray bends towards the normal. i r air water Incident ray Refracted ray normal i – angle of incidence r– angle of refraction
- 5. LIGHT When the light ray travels from water to air, the refracted ray bends away from the normal. i r air water Incident ray Refracted ray normal i – angle of incidence r– angle of refraction
- 6. LIGHT During refraction, light bends first on passing from air to glass and again on passing from the glass to the air.
- 7. LIGHT During refraction, light bends first on passing from air to glass and again on passing from the glass to the air. i r Incident ray Emergent ray Refracted ray Reflected ray air air glass
- 8. LIGHT Light slows down when it enters an optically denser medium. The refracted ray bends towards the normal when the second medium is optically more dense than the first. i r air water Incident ray Refracted ray normal
- 9. LIGHT Light speeds up when it enters an optically less dense medium. The refracted ray bends away from the normal when the second medium is optically less dense than the first. air water i r Incident ray Refracted ray normal
- 10. LIGHT Among the 3 transparent mediums (air, water and glass), glass has the highest optical density. air water i1 r1 Incident ray Refracted ray glass i2 r2 Refracted ray air water i1 r1 Incident ray glass i2 r2 Refracted ray Refracted ray
- 11. LIGHT Complete these ray diagrams. air glass glass water
- 12. LIGHT Complete these ray diagrams. airwater glassair
- 13. LIGHT The incident ray, the refracted ray and the normal at the point of incidence all lie in the same plane.
- 14. For two given media, the ratio sin i ÷ sin r is a constant, where i is the angle of incidence and r is the angle of refraction LIGHT i r air water Incident ray Refracted ray normal Refractive Index, n = sin i sin r
- 15. LIGHT The higher the optical density, the greater the refractive index. The greater the refractive index, the greater the bending of light towards the normal. air water i1 r1 Incident ray Refracted ray glass i2 r2 Refracted ray air water i1 r1 Incident ray glass i2 r2 Refracted ray Refracted ray
- 16. LIGHT If light is incident upon a piece of glass (refractive index 1.52) at an angle of 45o , what is the angle of refraction?
- 17. LIGHT Given that the refractive index of water is 1.33, calculate the angle of refraction when the incident ray comes in at 60o to the normal. 60o r air water Solution n = sin i sin r 1.33 = sin 60o sin r sin r = sin 60o 1.33 r = 40.6o
- 18. LIGHT When light travels from a less dense medium to a denser medium… n = sin i sin r i r air water When light travels from a denser medium to a less dense medium… n = sin r sin i i r air water
- 19. LIGHT The figure shows light travelling from water into the air. The ray is incident upon the boundary at 30o . What is the angle of refraction if the refractive index of water is 1.33? 30o r air water Solution n sin r sin i = 1.33 sin 30o sin r = sin r= 1.33sin 30o r = 41.9o
- 20. LIGHT Other ways of calculating the refractive index… Refractive index, n = Speed of light in vacuum / air Speed of light in medium = c v
- 21. LIGHT Take a look at this...
- 22. LIGHT The critical angle is the angle of incidence in the optically denser medium for which the angle of refraction is 90o . When i = critical angle,c r = 90o .
- 23. LIGHT This is called TOTAL INTERNAL REFLECTION. When i > critical angle, the ray gets reflected internally.
- 24. LIGHT For TOTAL INTERNAL REFLECTION to take place: The light ray must travel from an optically denser medium towards a less dense one. The angle of incidence must be greater than the critical angle. Direction of light path i
- 25. LIGHT How do we calculate the critical angle? We know that r = 90o …
- 26. LIGHT We know that when light travels from a less dense medium to a denser medium Refractive Index, n = sin r sin i We know that when light travels from a denser medium to a less dense medium Refractive Index, n = sin r sin i
- 27. LIGHT How do we calculate the critical angle? We know that r = 90o … Refractive Index, n = sin r sin i n = sin c sin 90o = sin c 1
- 28. LIGHT How do we calculate the critical angle? n =sin c =c 1 sin-1 n 1
- 29. LIGHT Medium: Refractive Index: Critical Angle: =c sin-1 n 1 Glass 1.50 = sin-1 1.50 1 = 41.8o
- 30. LIGHT Medium: Refractive Index: Critical Angle: =c sin-1 n 1 Water 1.33 = sin-1 1.33 1 = 48.8o
- 31. LIGHT Medium: Refractive Index: Critical Angle: =c sin-1 n 1 Diamond 2.42 = sin-1 2.42 1 = 24.4o
- 32. LIGHT Total Internal Reflection in Prisms
- 33. LIGHT Total Internal Reflection in Prisms