物理,pressure cooker

用戶91254

2013-06-24 12:15 am

A pressure cooker is a pot whose lid can be tightly sealed to prevent gas from entering or escaping.

If an otherwise empty pressure cooker is filled with air of room temperature and then placed on a hot stove, what would be the magnitude of the net force F120 on the lid when the air inside the cooker had been heated to 120∘C? Assume that the temperature of the air outside the pressure cooker is 20∘C (room temperature) and that the area of the pressure cooker lid is A. Take atmospheric pressure to be p_a.

Treat the air, both inside and outside the pressure cooker, as an ideal gas obeying pV=Nk_BT

答案係F120 = p_a*100/293*A

我知道293係(20+273=293K),但我唔明白既係100係點黎,同埋唔係好明白題目中既"magnitude of the net force F120"係指緊d咩,即係既然係net,咁應該係一d野減左另一樣野剩左落黎既野,但呢兩樣野又係指d咩呢?

請高手解答

回答 (1)

天同

2013-06-24 12:31 am

✔ 最佳答案

The net force, F120, is the difference between the force given by the hot air inside the pressure cooker and the force given by atmosphere outside the cooker. This is equal to the difference in pressure inside and outside the cooker multiplied by the area of the lid.

Using the Pressure Law to calculate the pressure P inside the cooker at 120'C,
P/(273+120) = Pa/(273+20)
i.e. P = 393(Pa)/293

Hence, difference in pressure = P - Pa = (393/293 - 1)Pa = 100(Pa)/293
Therefore, difference in force F120 = [100(Pa).A]/293

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