252CHAPTER 22 22.41(a) Snell’s law can be written as 122sinsinvv1θ=. At the critical angle of incidence ()1c=, the angle of refraction is 90° and Snell’s law becomes 12sincvv=. At the concrete-air boundary, 1112343 m ssinsin10.71850 m scvv−−===°(b) Sound can be totally reflected only if it is initially traveling in the slower medium. Hence, at the concrete-air boundary, the sound must be traveling in air . (c) S, so the wall is a good mirror. ound in air falling on the wall from most directions is 100% reflected22.42The sketch at the right shows a light ray entering at the painted corner of the cube and striking the center of one of the three
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