Refraction of light

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1. PHYSICS Refraction Of Light

2. Refraction Of Light When a ray of light , travelling through one medium strikes obliquely the surface of an other transparent medium, then there is change in its direction in the second medium. This change is called Refraction of light. Light refracts at boundary( b/w two mediums ) because of change in its speed.

3. Refraction Of Light If ray of light enters from rare into denser medium it bends towards the normal. But when enters from denser into rare medium, it bends away from the normal.

4. air glass e.g. from air to glass Light is bent towards the normal. incident ray normal refracted ray From a less dense to a denser medium

5. air water From a denser to a less dense medium e.g. from water to air Light is bent away from the normal. incident ray refracted ray normal

6. air glass Useful words to describe refraction of light normal incident ray angle of refraction angle of incidence refracted ray

7. Laws Of Refraction Of Light Incident ray, refracted ray and normal lie in the same plane. The ratio of sine of angle of incident to the sine of angle of refraction is constant in any two transparent mediums, which is termed refractive index (n). Refractive index (n) =sin Li/Sin Lr = Constant

8. Angle of Incidence (degrees) Angle of Refraction (degrees) 0.00 0.00 5.00 3.8 10.0 7.5 15.0 11.2 20.0 14.9 25.0 18.5 30.0 22.1 35.0 25.5 40.0 28.9 45.0 32.1 50.0 35.2 55.0 38.0 60.0 40.6 65.0 43.0 70.0 45.0 75.0 46.6 80.0 47.8 85.0 48.5  

9. Refraction of light

10. Refractive index and speed of light distance that light travel in 1 s vacuum (or air) 3  10 8 m water ( n = 1.33) 2.25  10 8 m glass ( n = 1.5) 2  10 8 m diamond ( n = 2.42) 1.25  10 8 m Refractive index Speed of light fastest slowest

11. Refractive Index (n) Of Different Materials

12. Prism It is transparent body (Glass) , commonly having three sides rectangular and two sides triangular.

13. Refraction Of Light Through Prism Incident ray PQ strikes side AB of prism. Inside prism the ray in shape of refracted ray QR, bends towards the normal XY . Then emergent ray RS coming from prism bends away from the normal LM.

14. Refractive Index Of Glass Prism (n G ) (n G )= Sin (A + D m ) 2 Sin A 2 LA = Angle of prism. LD m = Angle of minimum deviation. nG = Refractive index of glass prism

15. Refraction of light through prism

16. Total Internal Reflection If ray of light passes from a denser medium( water ) into a rare medium (air ) then it bends away from the normal. Now increasing the angle of incidence, angle of refraction also increases.

17. Total Internal Reflection At certain stage the angle of incidence has increased so much that the corresponding value of angle of refraction becomes equal to 90 o and refracted ray lies on the surface of denser medium. The angle of incidence for which the angle of refraction is 90 o is called the critical angle.

18. Total Internal Reflection Now if the value of angle of incidence is increased so much that it becomes greater than critical angle, then there is no more refraction but whole of it is reflected back in the denser medium. Such reflection of light is called total internal reflection.

19. Optical Fibres These are very thin, flexible glass rods, used for carrying light by total internal reflection from one end to other end. A bundle of optical fibres is called light pipe.

20. Optical Fibres The glass cladding of slightly lower refractive index than that of the core, prevents surface damage to the core fibre, otherwise would allow light to escape.

21. Optical Fibres (uses) Big advantage of an optical fibre is its small size and weight. Optical fibres are successfully used in internal surgery to examine body cavities and in telecommunication.

22. Lens & Its Kinds LENS = It is a transparent body(glass), bounded by one or two Curve surfaces. KINDS OF LENS = there are two kinds of lens (a) Convex Lens & (b) Concave Lens

23. Convex Lens It is thickest in the centre, because its boundaries are curving outwards. As it bends light inwards( rays come together), hence it is also called Converging lens. Its focal length is taken +ve. It forms real image.

24. Double convex lens behaves like two prisms with attached bases.

25. Concave Lens It is thinnest in the centre, because its boundaries are curving inwards. As it spreads light out( rays move apart), hence it is also called a diverging lens. Its focal length is taken –ve. It forms virtual image.

26. Uses Of Lenses Convex lens is used in camera,projectors,binocular,telescope,microscope,spectacle and as magnifier etc. Concave lens is used in spectacle for removing eye defect.

27. Convex Lens Used As Magnifier

28. Astronomical Telescope Camera Compound microscope Spectacle Binocular

29. Film Projector Slide Projector Over Head Projector

30. Images Formed By Convex Lens

31. Images Formed By Convex Lens

32. Magnification & Sign Conventions For Lenses Optical magnification is the ratio between the size of image & size of object. M = h i = q h o p M = Magnification, h i = Height of image , h o = Height of object. Distance b/w concave lens & image (q ) is taken - ve. Distance b/w convex lens & image( q ) is taken + ve. Focal length of concave lens ( f ) is taken - ve. Focal length of convex lens( f ) is taken + ve .

33. Power Of Lens Power of lens is the reciprocal of the focal length expressed in meters. Power = 1 Or P = 1 focal length (in m ) f The unit of refractive power of a lens is the diopter( where 1 diopter = !/meter ). Converging lens has a positive power and diverging lens has a negative power. One diopter is the power of lens of focal length one meter. A Powerful lens deviates light rays more and thus has a short focal length. Magnifying glass( of f=2cm) has power diopters,while high power microscope objective(of f= 4mm) has power 250 diopters.

34. Human Eye In eye image is formed on retina. In it amount of light entering into eye is controlled by Iris. For correct and clear image ( of near or far objects) the thickness of eye’s lens is increased or decreased by ciliary muscles.

35. Structure Of Human Eye

36. Short- Sightedness(Myopia ) Definition = In this defect of vision an eye can see clearly only near objects, Reason = the lens of eye becomes too much convergent, or eye ball becomes too long. So the images of distant objects is formed in front of the Retina. Remedy = For correcting this defect concave lens ( diverging lens) of suitable focal length is used.

37. Long- Sightedness (Hyperopia ) Definition =In this defect of vision, an eye can see clear only distant objects. Reason = the lens of eye becomes less convergent or eye ball becomes too short. Remedy = for removing this defect convex lens(converging lens) of suitable focal length is used.

38. Contact Lens

39. Astronomical Telescope It is used to see far objects near and clear In it the focal length of object lens is long and focal length of eye piece is short. Objective lens forms real inverted image before eye piece, which forms its magnified ,virtual image

40. Astronomical Telescope

41. Enlarged – Image is larger than actual object. Reduced – Image is smaller than object

42. Compound Microscope It is used to see minute near object clear and magnified. In it the focal length of objective lens is short and focal length of eye piece is long. Objective lens forms, enlarged ,inverted image, eye piece forms its further enlarged, virtual image.

43. Compound Microscope

44. Camera In it image is formed on sensitive film. Light reaching the film is controlled by shutter and also by diaphragm. For getting correct and clear image, convex lens is moved forward or backward.

45. Slide Projector

46. Camera

47. Lens Equation ( Convex Lens ) [As BD= p,DF= f & DI = q.] As Δ OID and Δ ABD are similar AB/OI = BD/DI……………….(I) AS Δ CDF and Δ OIF are similar CD/OI = DF/IF As CD = AB Then AB/OI = DF/IF ……………(II)

48. Lens Equation ( Convex Lens ) [As BD= p,DF= f & DI = q.] As Δ OID and Δ ABD are similar AB/OI = BD/DI……………….(I) AS Δ CDF and Δ OIF are similar CD/OI = DF/IF As CD = AB Then AB/OI = DF/IF ……………(II) comparing I and II we get. BD/DI = DF/IF or BD/DI = DF/DI –DF……………….(III) Put value of BD,DF and DI in equation III we get p/q =f/q-f B.C.M we get pq- pf = qf or pq=qf+ pf. Dividing both sides of above Equation by pqf we get pq/pqf = qf/pqf + pf/pqf 1/f = 1/p + 1/q (Lens Equation)

49. Thanks