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# Reflection and Refraction Practice Test

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By McGraw-Hill Professional
Updated on Oct 3, 2011

Review the following concepts if needed:

## Reflection and Refraction Practice Test

Refer to the text in this chapter if necessary. A good score is eight correct. Answers are in the back of the book.

1. A step-index optical fiber has a transparent core surrounded by a cladding, also transparent, but having a different index of refraction from the core (Fig. 10-10). Suppose that the core of a particular length of optical fiber has a refractive index of 1.45, while the cladding has a refractive index of 1.60, for red light. What is the maximum angle θ, relative to a line along the boundary between the core and the cladding and running parallel to the center of the fiber, at which a ray of red light inside the core can strike the boundary and be reflected back into the core?

(a) 25°

(b) 42°

(c) 65°

(d) There is no such angle because this fiber is improperly designed. The ray will pass from the core into the cladding no matter what the angle at which it strikes

Fig. 10–10. Illustration for quiz questions 1 and 2.

2. Suppose that the core of the optical fiber shown in Fig. 10-10 has a refractive index of 1.60 while the cladding has a refractive index of 1.45 for red light. What is the maximum angle θ, relative to a line along the boundary between the core and the cladding and running parallel to the center of the fiber, at which a ray of red light inside the core can strike the boundary and be reflected back into the core?

(a) 25°

(b) 42°

(c) 65°

(d) There is no such angle because this fiber is improperly designed. The ray will pass from the core into the cladding no matter what the angle at which it strikes

3. Suppose a pane of crown glass, with a refractive index of 1.52, is immersed in water, which has a refractive index of 1.33. A ray of light traveling in the water strikes the glass at 45° relative to the normal to the glass surface, and travels through the pane. What angle, relative to the normal, will the ray of light subtend when it leaves the pane and re-enters the water?

(a) 38°

(b) 54°

(c) 45°

(d) The light will never enter the glass. It will be reflected when it strikes the glass surface

4. Suppose a pane of flint glass, with a refractive index of 1.65, is immersed in water, which has a refractive index of 1.33. A ray of light traveling in the water strikes the glass at 80° relative to the normal, and travels through the pane. What angle, relative to the normal, will the ray of light subtend relative to the normal inside the glass?

(a) 38°

(b) 53°

(c) 65°

(d) The light will never enter the glass. It will be reflected when it strikes the glass surface

5. Imagine a mineral that is clear, and that has an index of refraction equal to exactly 1.80 for all colors of visible light. A prism made from this mineral will

(a) produce a well-defined, spread-out rainbow spectrum

(b) work only underwater

(c) not bend light rays passing through it

(d) none of the above

6. Ideal conditions for a “water mirage” over dry land that looks like a pond as a result of reflection exist when the index of refraction of the air near the ground is

(a) higher than that of the air above it

(b) lower than that of the air above it

(c) the same as that of the air above it

(d) at least as great as the index of refraction of water

7. Imagine the June solstice, when the sun’s rays constantly subtend an angle of 23.5° relative to the plane of the earth’s equator (Fig. 10-11). Suppose there is a perfectly smooth pond at 43.5° north latitude, and the sun strikes the surface of the pond at high noon. At what angle, relative to a line normal to the surface of the pond, will the sun’s rays shine down into the water? Assume the water has a refractive index of 1.33.

(a) 75°

(b) 27°

(c) 63°

(d) 15°

Fig. 10-11. Illustration for quiz question 7.

8. Imagine a solid globe of glass illuminated by monochromatic (singlecolored) light, as shown in Fig. 10-12. Suppose that the index of refraction of the glass is 1.55 throughout the globe. Also suppose that the light source is so distant that the rays can be considered parallel, and that the globe is surrounded by air. Inside the globe, the light rays

Fig. 10–12. Illustration for quiz questions 8 and 9.

(a) diverge

(b) converge

(c) remain parallel

(d) scatter at random

9. Suppose that the glass globe in Fig. 10-12 is placed in a clear liquid whose index of refraction is 1.75. Suppose the light rays are all parallel inside that liquid medium. Which of the following statements is true?

(a) All of the light rays are reflected from the surface back into the liquid

(b) Some of the rays penetrate into the globe, and some are reflected from the surface back into the liquid

(c) All of the rays penetrate into the globe, and they converge inside it

(d) All of the rays penetrate into the globe, and they diverge inside it

10. What is the critical angle, relative to the normal, of light rays inside a gem whose refractive index is 2.4? Assume the gem is surrounded by air.

(a) 25°

(b) 65°

(c) 67°

(d) 90°

1. d

2. a

3. c

4. b

5. d

6. b

7. d

8. b

9. b

10. a

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