Physics 213 General Physics Lecture 15 0

2 Last Meeting: Electromagnetic Waves, Maxwell Equations Today: Reflection and Refraction of Light

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The color of an object we see depends on two things: The kind of light falling on it and nature of its surface For instance, if white light is used to illuminate an object that absorbs all color other than red, the object will appear red. What color will the object show if green light is used instead? A white object reflects light of all wavelengths equally well, a black object, on the other hand, absorbs light of all wavelengths, and it appears black no matter what color light reaches it.

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QUICK QUIZ 22.1 Which part of the figure below shows specular reflection of light from the roadway?

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17 LD (Cinema Classics)  C: # 61 (Cars on Carpet)  C: # 66 (Swimming Pool)

18 Question: When you look down into a swimming pool, are you likely to underestimate or overestimate its depth? Answer: The pool appears shallower than it is.

19 QUICK QUIZ 22.3 A material has an index of refraction that increases continuously from top to bottom. Of the three paths shown in the figure below, which path will a light ray follow as it passes through the material?

20 QUICK QUIZ 22.3 ANSWER (b). When light goes from one material into one having a higher index of refraction, it refracts toward the normal line of the boundary between the two materials. If, as the light travels through the new material, the index of refraction continues to increase, the light ray will refract more and more toward the normal line.

21 Question: When a beam of light enters one medium from another, a quantity that never changes is its (a)direction (b)speed (c)frequency (d)wavelength Answer: c

22 QUICK QUIZ 22.4 ANSWER (c). Both the wave speed and the wavelength decrease as the index of refraction increases. The frequency is unchanged.

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27 Observing the Rainbow If a raindrop high in the sky is observed, the red ray is seen A drop lower in the sky would direct violet light to the observer The other colors of the spectra lie in between the red and the violet

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Dispersion by drops of water. Red is bent the least so comes from droplets higher in the sky.

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