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Unformatted text preview: CHAPTER 25 THE REFLECTION OF LIGHT: MIRRORS CONCEPTUAL QUESTIONS _____________________________________________________________________________________________ 1. SSM REASONING AND SOLUTION A sign painted on a store window is reversed when viewed from inside the store. A person inside the store views the sign in a plane mirror. As discussed in the text, the image of an object formed in a plane mirror is upright, has the same size as the object, is located as far behind the mirror as the object is in front of it, and is reversed left to right. Therefore, since the image is reversed left to right, the image of the sign painted on the store window, when viewed in a plane mirror in the store, will appear as it does when viewed from outside the store. ____________________________________________________________________________________________ 2 . REASONING AND SOLUTION As discussed in the text, the image of an object formed in a plane mirror is reversed left to right. If a clock is held in front of a mirror, its image is reversed left to right, but not up and down. In order to understand the appearance of the image of the second hand, as viewed by a person looking into the mirror, imagine replacing the second hand by a rotating vector that always points away from its rotation axis. At any instant, this vector can be resolved into horizontal and vertical components. Since the image is reversed left to right, the image of the horizontal component will be reversed in direction. In contrast, since the image is not reversed up and down, the image of the vertical component will point in the same direction as the object. Therefore, when the horizontal and vertical components of the image are combined, the resultant will rotate counterclockwise . Thus, from the point of view of a person looking into the mirror, the image of the second hand of the clock rotates in the counterclockwise direction. ____________________________________________________________________________________________ 3 . REASONING AND SOLUTION When parallel rays of light strike a concave mirror, they are reflected; these reflected rays converge at the focal point of the mirror. When parallel rays of light strike a convex mirror, they are also reflected; these reflected rays diverge from the mirror's surface and appear to originate from the focal point located behind the mirror. a. The earth-sun distance is very large; therefore, when rays of light from the sun reach the earth, they are essentially parallel. If it is desired to start a fire with sunlight, it is necessary to focus the parallel light rays from the sun on a very small area, preferably a point, on the piece of paper. Since a concave mirror reflects parallel rays so that they converge in front of the mirror, a concave mirror, rather than a convex mirror, should be used....
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