# Ch26 - CHAPTER 26 THE REFRACTION OF LIGHT LENSES AND OPTICAL INSTRUMENTS ANSWERS TO FOCUS ON CONCEPTS QUESTIONS 1(c When the light is refracted

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CHAPTER 26 THE REFRACTION OF LIGHT: LENSES AND OPTICAL INSTRUMENTS ANSWERS TO FOCUS ON CONCEPTS QUESTIONS 1. (c) When the light is refracted into liquid B it is bent away from the normal, so that n A > n B . When the light is refracted into liquid C it is bent toward the normal, so that n C > n A . Therefore, we conclude that n C > n A > n B . 2. 1.41 3. (b) When the light is refracted into liquid B it is bent away from the normal, so that n A > n B . When the light is refracted into liquid C it is also bent away from the normal, so that n A > n C . However, the bending is less than that in liquid B. Thus, the index of refraction of liquid C is closer to that of liquid A than the index of refraction of liquid B is. In fact, if n A and n C were equal, the ray would not be bent at all upon entering liquid C. This means that n C > n B . Therefore, we conclude that n A > n C > n B . 4. 4.41 cm 5. (d) The apparent depth d is given by 1.00 d d n ′ = , according to Equation 26.3, where d is the actual depth and n is the refractive index of the liquid. Thus, the apparent depth and the refractive index are inversely proportional, which means that the ranking in descending order is n C , n B , n A . 6. (c) Material B has the smaller refractive index. Therefore, a light ray that begins in material B and travels toward material A, with its greater refractive index, is bent toward the normal (not away from it) when it crosses the interface. 7. (a) When light travels from a material with a greater refractive index toward a material with a smaller refractive index, total internal reflection occurs at the interface when the angle of incidence is greater than the critical angle. Here, Equation 26.4 reveals that the critical angle for the glass-air interface is 1 c 1.00 sin 41.1 1.52 θ - = = ° . At point A the angle of incidence is 35º and is less than the critical angle. Therefore, some light passes into the air at point A. At

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69 THE REFRACTION OF LIGHT: LENSES AND OPTICAL INSTRUMENTS point B, however, total internal reflection occurs, because the angle of incidence is 55º and exceeds the critical angle. 8. 67.5 degrees 9. (d) The displacement occurs because of the refraction or bending of the ray that occurs when the ray enters and leaves the glass. The bending is greater when the refractive index is greater. Hence, the displacement is greatest for violet light. 10. (b) Equation 26.4 reveals that the critical angles for the glass-air interface are 1 c, red 1.000 sin 41.14 1.520 θ - = = ° and 1 c, violet 1.000 sin 40.56 1.538 - = = ° . The angle of incidence shown is 40.85º, which is greater than the critical angle for violet light, but less than the critical angle for red light. Therefore, only red light enters the air, the violet light being totally internally reflected.
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## This note was uploaded on 03/30/2012 for the course PHYSICS 201 taught by Professor Rollino during the Fall '11 term at Rutgers.

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Ch26 - CHAPTER 26 THE REFRACTION OF LIGHT LENSES AND OPTICAL INSTRUMENTS ANSWERS TO FOCUS ON CONCEPTS QUESTIONS 1(c When the light is refracted

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