873 Chapter 31 Properties of Light Conceptual Problems 1 • Determine the ConceptThe population inversion between the state E2,Neand the state 1.96 eV below it (see Figure 31-9) is achieved by inelastic collisions between neon atoms and helium atoms excited to the state E2,He.2 •• Determine the ConceptAlthough the excited atoms emit the light of the same frequency on returning to the ground state, the light is emitted in a random direction, not exclusively in the direction of the incident beam. Consequently, the beam intensity is greatly diminished.3 •Determine the ConceptThe layer of water greatly reduces the light reflected back from the car’s headlights, but increases the light reflected by the road of light from the headlights of oncoming cars.4 •Determine the ConceptWhen light passes from air into water its wavelength changes (waterairwaternλλ=), its speed changes (waterwaterncv=), and the direction of its propagation changes in accordance with Snell’s law. correct.is)(c*5 •• Determine the Concept The change in atmospheric density results in refraction of the light from the sun, bending it toward the earth. Consequently, the sun can be seen even after it is just below the horizon. Also, the light from the lower portion of the sun is refracted more than that from the upper portion, so the lower part appears to be slightly higher in the sky. The effect is an apparent flattening of the disk into an ellipse.6 • Determine the Concept (a) Yes. (b) Her procedure is based on Fermat’s principle in that, since the ball presumably travels at constant speed, the path that requires the least time of travel corresponds to the shortest distance of travel.7 • Determine the Concept Because she can run faster than she can swim, she should choose the path that will maximize her running distance. Path LESis the path that satisfies this criterion.
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