Question

(a) Briefly explain what is meant by the following terms: refraction, refractive index, angle of incidence, angle of refraction. [4 marks] (b) The drawing shows four different situations in which a light ray is traveling from one medium into another. In some of the cases, the refraction is not shown correctly. For cases (i), (ii), and (iii), the angle of incidence is 55°; for case (iv), the angle of incidence is 0°. Identify which cases are incorrectly drawn and determine the angle of refraction in each case. [8 marks] n21.6 1.5 n2 1.6 1 1.6 21.4 (iv) (c) Imagine light travels through a material with a smaller refractive index toward a material with a larger refractive index. What is the phase change in the ray that is reflected at the [2 marks] boundary between both materials? (d) A transparent film (n - 1.20) is deposited on a glass plate (n-1.52) to form a non- reflective coating. The film has a thickness of 1.02 x 10-7m. What is the longest possible wavelength (in vacuum) of light for which this film has been designed? (Hint: Consider the phase shifts of the beams reflected from the top and the bottom of the film, respectively. Add those to the extra distance travelled by the wave within the film. Then establish the condition for destructive interference and find the longest wavelength for this condition.) |6 marks]

Answer 1

Refraction rightarrow when light passes from one medium to another (say from air, water to glass etc) part is reflected back into the first medium & the rest passes in to the another medium it bends towards the normal or away, from the normal means its direction is changed this phenomenon is know as Refraction. Refractive index(r): the constant ratio sin i_1/sin i_1 is called refractive index for Ex -if light passing from the first to the second medium (or refractive index of 2 with respect to 1) it is denoted by mu_2 thus, mu_2 = sin i_1/sin i_2 angle of incidence: Angle formed by incidence light with normal is called angle of incidence Angle of refraction: - Angle formed by refracted light with normal is called angle of refraction b) in fig (i), (ii), (iii) & (iv) fig (ii)& (iv) is wronge fig (iii) is wronge because when light move from light medium to denser medium
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