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Unformatted text preview: 100 TEMPERATURE AND HEAT CHAPTER 12 TEMPERATURE AND HEAT CONCEPTUAL QUESTIONS ____________________________________________________________________________________________ 1. REASONING AND SOLUTION The length L of the tape rule changes by an amount L when its temperature changes by an amount T, where L is given by L = L T and is the coefficient of linear expansion. When the length of the tape rule changes, the location of the graduations changes and makes the rule inaccurate. For year-round outdoor use, the range of T will be large; therefore, to minimize the thermal expansion of the rule we would want the rule to be made from a material with a small coefficient of linear expansion. Since the coefficient of linear expansion of steel is less than that of aluminum, we would choose a steel tape rule for highest accuracy. ____________________________________________________________________________________________ 2 . REASONING AND SOLUTION The distance between the two fine lines engraved near the ends of the bar is unique only at a specified temperature. When the temperature of the bar is raised, the length of the bar increases, and the distance between the engraved lines increases. Since the bar was an international standard for length, it was essential that the distance between the lines always remained the same; therefore, it was important that the bar be kept at a constant temperature. ____________________________________________________________________________________________ 3 . REASONING AND SOLUTION The plate is made of aluminum; the spherical ball is made of brass. The coefficient of linear expansion of aluminum is greater than the coefficient of linear expansion of brass. Therefore, if the plate and the ball are heated, both will expand; however, the diameter of the hole in the aluminum plate will expand more than the diameter of the brass ball. In order to prevent the ball from falling through the hole, the plate and the ball must be cooled. Both the diameter of the hole in the plate and the diameter of the ball will contract. The diameter of the hole will decrease more than the diameter of the ball, thereby preventing the ball from falling through the hole. ____________________________________________________________________________________________ 4 . REASONING AND SOLUTION Reinforced concrete is concrete that is reinforced with embedded steel rods. For this arrangement to be practical, it is essential that the coefficient of linear expansion of concrete is the same as that of steel. When the reinforced concrete is heated or cooled, both the concrete and the steel must expand or contract by the same amount. If the coefficients of linear expansion were not the same, the concrete and steel would expand and contract at different rates when heated or cooled. If the steel expanded or contracted more than the concrete, it would place internal stresses on the concrete, thereby causing it to weaken and possibly crack. causing it to weaken and possibly crack....
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