Physics 21 Fall, 2004 Solution to HW-23 33 P6 The speed of light in a certain substance is 92 per-cent of its value in water. What is the index of refraction of that substance? From Table 33-1 in the text, n in water is 1.33, so v water = c 1 . 33 . In the substance, n = c v = c0 . 92 v water = c0 . 92( c/ 1 . 33) = 1 . 33 . 92 =1 . 45 33 P10 A person whose eyes are 1.54 m above the ﬂoor stands 2.30 m in front of a vertical plane mirror whose bot-tom edge is 40 cm above the ﬂoor. What is the horizontal distance x to the base of the wall supporting the mirror of the nearest point on the ﬂoor that can be seen reﬂected in the mirror? 1.14 m θ θ θ The diagram shows the three angles that must be the same; the length of the 1.14 m line is determined from (1 . 54 −0 . 40) m. Then tan θ = 1 . 14 2 . 30 =0 . 40 x ⇒ x = 2 . 30 ×0 . 40 1 . 14 =0 . 81 m 33 P18 If you look at yourself in a shiny Christmas tree ball with a diameter of 9.0 cm when your face is 25.0 cm away from it, where is your image? Is it real or virtual? Is
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