Ques1) Rubber has a negative average coefficient of linear expansion.
What happens to the size of a piece of rubber as it iswarmed?
Ques2) An inflated rubber balloon filled with air is immersed in a flask of liquid nitrogen that is at 77 K. Describe what happens to the balloon, assuming that it remains flexible while being cooled ?
Ques3) The pendulum of a certain pendulum clock is made of brass. When the temperature increases, does the clock run too fast, run too slowly, or remain unchanged?
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4 Answers
391) i have a diff explanation:
When rubber is heated it behaves differently than most familiar materials. Most materials expand when they are heated. Consider the liquid in a thermometer. The thermometer works because the liquid expands when its temperature increases. Similarly, a wire made of metal, such as copper, becomes longer as it gets hotter. The expansion of metals with increasing temperature is the principle behind the functioning of home thermostats and of jumping discs.
Whether a material expands or contracts when it is heated can be ascribed to a property of the material called its entropy. The entropy of a material is a measure of the orderliness of the molecules that make up the material. When the molecules are arranged in an ordered fashion, the entropy of the material is low. When the molecules are in a disordered arrangement, the entropy is high. (An ordered arrangement can be thought of as coins in a wrapper, while a disordered one as coins in a tray.) When a material is heated, its entropy increases because the orderliness of its molecules decreases. This occurs because as a material is heated, its molecules move about more energetically. In materials made up of small, compact molecules, e.g., the liquid in a thermometer, as the molecules move about more, they push their neighboring molecules away. Rubber, on the other hand, contains very large, threadlike molecules. When rubber is heated, the sections of the molecules move about more vigorously. In order for one part of the molecule to move more vigorously as it is heated, it must pull its neighboring parts closer. To visualize this, think of a molecule of the stretched rubber band as a piece of string laid out straight on a table. Heating the stretched rubber band causes segments of the molecules to move more vigorously, which can be represented by wiggling the middle of the string back and forth. As the middle of the string moves, the ends of the string get closer together. In a similar fashion, the molecules of rubber become shorter as the rubber is heated, causing the stretched rubber band to contract
393)
As the temperature increses, the length of the pendulum also increases. With an increased length, the period of the pendulum is also increased. As the pendulum oscillates more slowly, the clock keeps time more slowly.
3Q2)i think it shud contract.
let us take the inflated rubber balloon as a system,this is an example of closed system,Since the rubber balloon is free to expand even at low temperature so we can say dat the pressure of our system doesnt changes,and our system now follows the law V=kT .Since the temperature of our system starts to decrease until a steady state is reached between the liquid nitrogen and our system.