question_answer 40)

  You are given four sources of light each one providing a light of a single colour - red, blue, green and yellow. Suppose the angle of refraction for a beam of yellow light corresponding to a particular angle of incidence at the interface of two media is 90°. Which of the. following statements is correct if the source of yellow light is replaced with that of other lights without changing the anlge of incidence ? (a) The beam of red light would undergo total internal reflection (b) The beam of red light would bend towards normal while it gets refracted through the second medium (c) The beam of blue light would undergo total internal reflection (d) The beam of green light would bend away from the normal as it gets refracted through the second medium

Answer:

  (c) Here, for yellow light, r = 90° when i = C. As i  is kept same, C must be smaller for total internal reflection. From  will be smaller, when u is larger. Out of given colours,   is largest for sine blue colour. Critical angle will be smallest for blue colour. Therefore, blue light would undergo total internal reflection. choice (C) is correct.