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Physics...

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1. Advantage of using the freezing point and the boiling point of pure water as fixed points in the Celsius scale?2. Why is it essential to ensure that pure water is used?3. A metal wire has a resistance of 30Ω when it is placed in a glass of pure melting ice. When its temperature rises to 25?c, its resistance... 顯示更多 1. Advantage of using the freezing point and the boiling point of pure water as fixed points in the Celsius scale? 2. Why is it essential to ensure that pure water is used? 3. A metal wire has a resistance of 30Ω when it is placed in a glass of pure melting ice. When its temperature rises to 25?c, its resistance increases to 42Ω. What is the resistance of the wire when it is placed in pure boiling water? Assume that the resistance of the wire increases linearly with the temperature.

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1. I think ... It's easier to calibrate the thermometer. 2. If there're impurities in the water, it may affect the b.p. and m.p. of the water. 3. Let xΩ be the resistance of the wire when it is placed in pure boiling water. (x-30) / (42-30) = 100 / 25 x=78 Therefore, the resistance of the wire when it is placed in pure boiling water is 78Ω.

其他解答:

1.The two fixed points can be reproduced easily and accurately. 2.To insure the ice point and stream point won't affected by the other substances 3. resistance change for 1?c 42-30/25-0 =12/25 =0.48Ω when the water is in 100?c 0.48*100+30 =48+30 =78Ω