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Refraction at plane surface and Prisms

Refraction at plane surface and Prisms. Dr. M K Raghavendra BASE, Bangalore. Type 1 – Snell’s law and RI. Snell’s law:. Relative R I in terms of wavelength of light. Relative R I in terms of speed of light. Absolute R I in terms of speed of light.

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Refraction at plane surface and Prisms

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  1. Refraction at plane surface and Prisms Dr. M K Raghavendra BASE, Bangalore

  2. Type 1 – Snell’s law and RI Snell’s law: RelativeR I in terms of wavelength of light RelativeR I in terms of speed of light Absolute R I in terms of speed of light Relative R I in terms of absolute R I Modified Snell’s law Frequency remains constant

  3. A ray of light is incident on the interface of two media at an angle of 450and is refracted in to the other medium at an angle of 300. If the speed of light in the first medium is 3X108ms-1 ,what is the speed of light in the second medium? • 1.96X108ms-1 • 2.12X108ms-1 • 3.18X108ms-1 • (4) 3.33X108ms-1

  4. Snell’s law: Thus

  5. sin (r) 370 sin (i) O • 2)A ray of light is travelling from medium A to medium B. The angle of incidence is iand that of refraction is r. Graph between sin(i) and sin(r) is as shown in Figure below. We can conclude the following • (i) Speed of light in medium B is three-fourth of that in medium A. • (ii) Total internal reflection cannot take place. • (iii) Refractive index of medium B is greater than that of medium A. • Correct conclusions are • Only (i) and (ii) (2) Only (ii) and (iii) • (3) (i), (ii) and (iii) (4) Only (i) and (iii)

  6. sin (r) 370 sin (i) O The slope of the straight line: sin (r) sin (i) Medium B is denser than medium A Since nb> na TIR cannot take place

  7. 3) Given refractive index of glass with respect to air is ang= 3/2 and that of water with respect to air is anw= 4/3, the refractive index of glass with respect to water is • 8/9 • 9/8 • 2 • 1/2

  8. Lateral shift Type 2: Normal Shift and Lateral Shift Normal shift a) Object in denser b) Object in rarer

  9. 4) A vessel of height h is filled with a liquid of refractive index n1 to a height h/2 and the upper half of the vessel is filled with a liquid of refractive index n2. The apparent depth of the vessel as seen along the normal is • 1) 2) • 3) 4)

  10. In case of one liquid the apparent depth is given by In case of many layers of liquid

  11. D C B A • 5) A ray of light passes through four transparent media with refractive indices 123 and 4 as shown in the figure. The surfaces of all media are parallel. If the emergent ray CD is parallel to the incident ray AB, we must have • 1 = 2 • 2 = 3 • 3 = 4 • 4 =1

  12. Apply to medium 1 and medium 4 Since ray AB and CD are parallel, i1 and i4 are equal Implies 1 = 4

  13. 6) An ink dot on a paper placed on a table top is viewed from a distance of 30 cm above it with the help of a telescope. A 16 cm thick glass slab is placed on the ink dot. By what distance the telescope should be raised to refocus the ink dot ? The refractive index of glass is 1.6. • 3 cm • 4 cm • 5 cm • 6 cm

  14. The telescope should be moved up by a distance (y) equal to normal shift produced by the slab

  15. T H S H (H/2) • 7) Consider the situation shown in the figure. The bottom of the vessel is a plane mirror, S is a small fish located at a height of H/2 from the plane of the mirror, T is a human eye located at a height of H from the surface of water. The distances at which the fish sees the images of the eye (with respect to its position) are • 1) • 2) • 3) • 4)

  16. T H S H (H/2) Image 1 nH + H nH + H/2 Image 1: H (n+1/2) A.P = nH nH + H+H/2 Image 2: H (n+3/2) Image 2

  17. Type 3: Critical angle and Total Internal Reflection

  18. 8) A, B and C are three optical media of respective critical angles C1, C2 and C3. Total internal reflection of light can occur from A to B and also from B to C but not from C to A. Then the correct relation between critical angles is • C1>C2>C3 • (2) C1= C2= C3 • (3)C3> C1> C2 • (4)C1<C2<C3

  19. T I R can occur when light travels from medium A to medium B T I R can occur when light travels from medium B to medium C Therefore

  20. 9) What is the critical angle, C for calcite (=1.5) immersed in oil (=1.1)? • (1) • (2) • (3) • (4)

  21. Type 4: Prism, angle of deviation, minimum deviation

  22. 10) The minimum angle of deviation for a prism of refractive index 1.732 is equal to its refracting angle. What is the angle of prism? • 400 • (2) 450 • (3) 600 • (4) 300

  23. In this case A = D A/2 =300 Or A=60o

  24. 11) A ray of light is incident on one refracting face of a prism of angle 750. It passes through the prism and is incident on the other face at critical angle. If the refractive index of the material of the prism is √2, then the angle of incidence on the first face is • 300 • (2) 450 • (3) 600 • (4) 75 0

  25. We know that r1 + C =750 750 C = 450 r1 =300 r1 C

  26. Deviation Angular dispersion Type 5: Small angled prism , angular dispersion and dispersive power Dispersive power In case of C D F line

  27. 12) The dispersive power of the material of the prism for which refractive index for violet and red colours are nv = 1.524, nr = 1.514 respectively is • 0.025 • 0.034 • 0.019 • 0.015

  28. Dispersive power  is given by

  29. Dispersion with out deviation Type 6: Combination of Prisms Deviation with out dispersion

  30. 13) A crown glass prism of 60 is cemented with a flint glass prism to form a pair which produces dispersion without deviation. If the refractive index of the crown glass prism is 1.52 and that of flint glass 1.66, then the angle of flint glass pair should be • 4.730 • (2) 5.730 • (3) 6.730 • (4) 7.730

  31. Condition for dispersion with out deviation is

  32. Conceptual questions

  33. 14) Light appears to travel in straight line because • The frequency of light is very small • (2) Light consists of very small particles • (3) The wavelength of light is very small • (4) The velocity of light is different for different colours.

  34. 15) When light is refracted through a prism, maximum deviation occurs when the following conditions are satisfied • (i) the ray is incident grazing the first face • (ii) the ray emerges out grazing its second face • Options • Only in case (i) (2) Only in case (ii) • (3) In both the cases (4) Not under these cases

  35. 16) A man is swimming underwater with undisturbed surface. Looking up at a bright sky through the water, he will see • (1)a bright patch directly above whose angular size is • independent of the depth of the swimmer • (2)a shining surface of the water • (3) just darkness • (4) a bright patch directly above whose angular size depends • upon the depth of the swimmer

  36. C C

  37. All the best Thank You

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