s_chapter_20' - Chapter 20 Thermal Properties and Processes...

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Chapter 20 Thermal Properties and Processes Conceptual Problems 1 Why does the mercury level of a thermometer first decrease slightly when the thermometer is first placed in warm water? Determine the Concept The glass bulb warms and expands first, before the mercury warms and expands. 2 A large sheet of metal has a hole cut in the middle of it. When the sheet is heated, the area of the hole will ( a ) not change, ( b ) always increase, ( c ) always decrease, ( d ) increase if the hole is not in the exact center of the sheet, ( e ) decrease only if the hole is in the exact center of the sheet. Determine the Concept The heating of the sheet causes the average separation of its molecules to increase. The consequence of this increased separation is that the area of the hole always increases. ) ( b is correct. 3 [SSM] Why is it a bad idea to place a tightly sealed glass bottle that is completely full of water, into your kitchen freezer in order to make ice? Determine the Concept Water expands greatly as it freezes. If a sealed glass bottle full of water is placed in a freezer, as the water freezes there will be no room for the expansion to take place. The bottle will be broken. 4 The windows of your physics laboratory are left open on a night when the temperature of the outside dropped well below freezing. A steel ruler and a wooden ruler were left on the window sill, and when you arrive in the morning they are both very cold. The coefficient of linear expansion of wood is about 5 × 10 6 K 1 . Which ruler should you use to make the most accurate length measurements? Explain your answer. Determine the Concept You should use the wooden ruler. Because the coefficient of expansion for wood is about half that for metal, the metal ruler will have shrunk considerably more than will have the wooden ruler. 5 Bimetallic strips are used both for thermostats and for electrical circuit breakers. A bimetallic strip consists of a pair of thin strips of metal that have different coefficients of linear expansion and are bonded together to form one doubly thick strip. Suppose a bimetallic strip is constructed out of one steel strip and one copper strip, and suppose the bimetallic strip is curled in the shape of a circular arc with the steel strip on the outside. If the temperature of the strip is decreased, will the strip straighten out or curl more tightly? 1863
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Chapter 20 1864 Determine the Concept The strip will curl more tightly. Because the coefficient of linear expansion for copper (17 × 10 6 K 1 ) is greater than the coefficient of linear expansion for steel (11 × 10 6 K 1 ), the length of the copper strip will decrease more than the length of the steel strip resulting in a tighter curl. 6 Metal A has a coefficient of linear expansion that is three times the coefficient of linear expansion of metal B. How do their coefficients of volume expansion β compare? ( a ) A = B , ( b ) A = 3 B , ( c ) A = 6 B , ( d ) A = 9 B , ( e ) You cannot tell from the data given.
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s_chapter_20' - Chapter 20 Thermal Properties and Processes...

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