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On Boyle's Law

  1. Dec 6, 2003 #1
    Hello everyone!

    I have some questions here to ask.... I hope anyone could help me here. Here are the following.

    1. How would the presence of air bubbles or water in mercury affect the results in a "J-tube" experiment?

    2. Why does food cook faster in a pressure cooker than in an aluminum ware?

    3. There are times when the water boils at less than 100 deg. celsius, especially at mountainous regions. Why is it?
  2. jcsd
  3. Dec 6, 2003 #2

    Doc Al

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    Not sure what you mean. The air and water would rise to the top of the mercury. Kind of hard to mix mercury and water!
    Food cooks faster when you can get it hotter. At ordinary pressures, the boiling point of water is 100 degrees C; that's as hot as you can make it. By increasing the pressure (which is what a pressure cooker does) the water is harder to boil---the boiling point is hotter, so the food cooks faster.
    For the same reasoning as in #2. What prevents the water from just "boiling off" at any temperature? Air pressure. The more pressure, the hotter you have to make the water in order to get it to boil. On the mountains, pressure is less so you can't get the water as hot since it starts to boil sooner. Makes for a lousy cup of tea!
  4. Dec 6, 2003 #3
    1) Not quite sure if you would get such bubbles....... ?

    2) The high pressure means that the water boiling and steam inside are at a much greater temp (ie well over 100 deg) than if boiled in an open pan. Hence they cook quicker.

    3) The energetic water particles near the surface of the water can escape into the air as steam (ie boiling) much easier if there is a lower air pressure above the liquid surface. Water will boil at 70 deg or so up a tall mountain.
  5. Dec 6, 2003 #4
    Pretty identical answers there Doc Al! You beat me too it though...:smile:
  6. Dec 6, 2003 #5

    Doc Al

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    We'll call it a draw! At least we agree.
  7. Dec 7, 2003 #6


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    Air or water in the closed side of a "J"-tube can result in higher measured pressures in the closed side than those measured with "clean" mercury.
  8. Dec 7, 2003 #7
    On question 1

    Hello again...

    Thank you for all your helps. =)

    Well, I observed that when i am filling the J-tube with amounts of mercury, I could see some kind of "open holes" in it, which I am referring to it as air bubbles. =)

    I kept wondering, what happens if I didn't mind that?
  9. Dec 10, 2003 #8

    Hello everyone!

    Thank you. =)

    Another thing, my email tells me that I have received a reply

    from the physics forum, but when I went here, they don't appear.

    Why is it so?
  10. Dec 10, 2003 #9
    Have u Cliked the link provided by the email
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