DISPERSION VERY SHORT ANSWER QUESTIONS Q-1. What will be the spectrum of sun during a total solar eclipse? Q-2. Why the secondary rainbow is always fainter than the primary rainbow? Q-3. Two identical prisms made of the same material placed with their based on opposite sides (of the incident white light) and faces touching (or parallel) neither deviate nor disperse. Can this arrangement produce a parallel displacement of the beam? Q-4. What colour do you observe when white light passes through a blue and yellow filter? Q-5. People usually prefer light-coloured dresses during summer and dark dresses during winter. Why? Q-6. Does a beam of white light give a spectrum on passing through a hollow prism? Q-7. Name one essential condition for observing a rainbow. Q-8. What do you mean by the dispersive power of the material of a prism? Q-9. Q-10. For which colour, the refractive index of material of a prism is (i) minimum (ii) maximum Refractive indices of glass for blue, red and yellow colours are μ b, μ y and μ r respectively. Write these symbols in decreasing order of values. Q-11. Which colour deviates (i) most (ii) least on passing through a prism? Q-12. Is there any invisible spectrum? Q-13. Draw the diagram of the path of a ray of light suffering minimum deviation. Q-14. Out of red and blue lights, for which colour is the refractive index of glass greater? Q-15. Which has larger wavelength, violet or red colour? Q-16. Write the relation for the refractive index μ of the prism in terms of the angle of minimum deviation m and the angle A of prism. Q-17. Plot a graph to show the variation of the angle of deviation as a function of the angle of incidence for light rays passing through a prism. Show the point of minimum deviation. 1
Q-18. What are the factors on which angular dispersion of a prism depends? Q-19. On what factors does the dispersive power of a material depend? Q-20. What is dispersion of light? SHORT ANSWER QUESTIONS Q-21. Why is a rainbow not seen during the middle of the day? Q-22. In a rainbow, will the secondary rainbow appear above or below the primary rainbow? Why? Q-23. Can any two people see the same rainbow? Explain. Q-24. Why the secondary rainbow has inverted colours? Q-25. What is Cherenkov radiation? Q-26. What is the essential difference between fluorescence and phosphorescence? Q-27. Why one prefers even in summer a black umbrella to a white one? Q-28. What does a welder protect against when he wears a mask? Q-29. Do materials always have the same colour whether viewed by reflected light or through transmitted light? Q-30. How would a blue object appear under sodium lamp light? Q-31. Does a beam of light give spectrum on passing through a hollow prism containing air? Explain. Q-32. Rays of red and blue light are incident on a given prism. Which will have larger value of m, the angle of minimum deviation? 2
Q-33. A monochromatic ray of light is made to fall on a prism under minimum deviation condition. What is the relation between the angle of incidence and the angle of emergence? Q-34. Why does sky look blue? What will it look like on moon? Q-35. A glass slab is placed over a page in which letters are printed in different colours. Will the image of all the letters lie in the same plane? If not, which letter will appear to be raised maximum? Q-36. Why white light is dispersed when passing through a prism? Q-37. The eye is most sensitive to yellow colour. But the danger signals are red. Why? Q-38. A glass prism has a minimum angle of deviation m in air. State, with reason, how the angle of minimum deviation will change if the prism is immersed in a liquid of refractive index greater than 1. Q-39. Q-40. Q-41. Q-42. Why does the sky appear blue? Give reasons. Explain why the sun appears red at sunset. Rainbow is never observed on the surface of the moon. Why Why is the rising sun red in colour? Give reason. SHORT ANSWER QUESTIONS Q-43. Calculate the dispersive power for crown and flint glass from the following data : C D F Crown 1.5145 1.5170 1.5230 Flint 1.6444 1.6520 1.6637 Q-44. Find the angle of flint glass prism which produces the same angular dispersion for C and F wavelengths as a 10 0 crown glass prism. Q-45. Why the prism spectrum is spread out more at the violet end than at the red end? CONCEPTUAL PROBLEMS Q-46. Draw a ray diagram showing the formation of virtual image by a prism. 3
Q-47. A convex lens made of a variety of glass of high dispersive power has focal length of 15 cm. A parallel beam of white light is incident on one side of the lens and screen is placed on the other side. Describe the chromatic aberration of the lens i.e., describe the colours on the spot focused on the screen as the screen is moved away from the lens. Q-48. Red light is incident on a converging lens of focal length f. State with reason how f will change if red light is replaced by blue light? LONG ANSWER QUESTIONS Q-49. Derive prism formula for a standard prism. If the angle of prism is small, then what will be the form of prism formula? Q-50. Discuss the phenomenon of refraction through a prism and derive the relation μ = sin A+δm 2 sin A 2 where A is the angle of prism, μ is the refractive index of the material of the prism and m is the angle of minimum deviation. Q-51. Q-52. Derive prism formula for a prism of small angle. Write the relation between the angle of incidence (i), the angle of emergence (e), the angle of prism (A) and the angle of deviation ( ) for rays undergoing refraction through a prism. What is the relation between i and e for rays undergoing minimum deviation? Using this relation, write the expression for the refractive index (μ) of the material of a prism in terms of A and the angle of minimum deviation ( m ). 4
Q-53. Draw a ray diagram to show the refraction of light through a glass prism. Hence obtain the relation for the angle of deviation in terms of the angle of incidence, angle of emergence and the angle of the prism. 5