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Chapter 31

# Chapter 31 - Chapter 31 Properties of Light Conceptual...

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Chapter 31 Properties of Light Conceptual Problems 1 [SSM] A ray of light reflects from a plane mirror. The angle between the incoming ray and the reflected ray is 70 ° . What is the angle of reflection? ( a ) 70 ° , ( b ) 140 ° , ( c ) 35°, ( d ) Not enough information is given to determine the reflection angle. Determine the Concept Because the angles of incidence and reflection are equal, their sum is 70 ° and the angle of reflection is 35 ° . ( ) c is correct. 2 A ray of light passes in air is incident on the surface of a piece of glass. The angle between the normal to the surface and the incident ray is 40°, and the angle between the normal and the refracted ray 28°. What is the angle between the incident ray and the refracted ray? ( a ) 12°, ( b ) 28°, ( c ) 40° ,( d ) 68° Determine the Concept The angle between the incident ray and the refracted ray is the difference between the angle of incidence and the angle of refraction. () a is correct. 3 During a physics experiment, you are measuring refractive indices of different transparent materials using a red helium-neon laser beam. For a given angle of incidence, the beam has an angle of refraction equal to 28° in material A and an angle of refraction equal to 26° in material B. Which material has the larger index of refraction? ( a ) A, ( b ) B, ( c ) The indices of refraction are the same. ( d ) You cannot determine the relative magnitudes of the indices of refraction from the data given. Determine the Concept The refractive index is a measure of the extent to which a material refracts light that passes through it. Because the angles of incidence are the same for materials A and B and the angle of refraction is smaller (more bending of the light) for material B, its index of refraction is larger than that of A. b is correct. 4 A ray of light passes from air into water, striking the surface of the water at an angle of incidence of 45º. Which, if any, of the following four quantities change as the light enters the water: ( a ) wavelength, ( b ) frequency, ( c ) speed of propagation, ( d ) direction of propagation, ( e ) none of the above? 2889

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Chapter 31 2890 Determine the Concept When light passes from air into water its wavelength changes ( water air water n λ = ), its speed changes ( water water n c v = ), and the direction of its propagation changes in accordance with Snell’s law. Its frequency does not change, so () a , ( ) c and ( ) d change. 5 Earth’s atmosphere decreases in density as the altitude increases. As a consequence, the index of refraction of the atmosphere also decreases as altitude increases. Explain how one can see the Sun when it is below the horizon. (The horizon is the extension of a plane that is tangent to Earth’s surface.) Why does the setting Sun appear flattened? Determine the Concept The decrease in the index of refraction n of the atmosphere with altitude results in refraction of the light from the Sun, bending it toward the normal to the surface of Earth. Consequently, the Sun can be seen even after it is just below the horizon.
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