The speed of light in a glass is 2.0 108 ms1. 3
c2 2 3 108
Qc2 2 3 (3 108) 2 108
EXERCISE 13.1 REFRACTIVE INDEX Take the refractive index of water as in all these questions.
Q1 A 1 coin is at the bottom of a swimming pool of depth 2.1 m. How far from the surface of the water does the coin appear to be, when viewed from directly above the coin?
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Q2 When light enters a glass prism with angle of incidence 39°, it bends towards the normal and has an angle of refraction of 24.8°. (i) What is the refractive index of the glass? (ii) If light were to enter the same prism from water rather than air, how would it affect the path of the refracted ray? Make reference to angle of refraction. (iii) What is the refractive index of water to glass?
Q3 A ray of light strikes at a plastic prism with an angle of incidence of 39.9°. It has an angle of refraction of 24.8°. (i) What is the refractive index of the prism? (ii) Draw a diagram of light entering the prism from water.
Q4 Given that the refractive index of diamond is , calculate the speed of light in diamond.The speed of light in air is 3 108 m s1.
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Total Internal Reflection TOTAL INTERNAL REFLECTION
Total internal reflection is the optical phenomenon where light is reflected back from a boundary between two media; it occurs when the light travelling towards the rarer medium from the denser one, striking the boundary with an angle of incidence greater than the critical angle for those two media.
Critical Angle CRITICAL ANGLE
The critical angle is the angle of incidence in the denser medium which causes an angle of refraction of 90°.
Explanation
When light travels from a denser medium into a rarer one, it is refracted away from the normal. As the angle of incidence increases, so does the angle of refraction.
Eventually a stage is reached when the angle of refraction is 90. The angle of incidence for which this occurs is called the critical angle (C) for those two media.
