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Heat Energy in a Pan

  1. Jun 28, 2013 #1
    "Explain how energy gets from the flame of a gas cooker to the contents of a pan of water above the flame".

    This has stumped me...I've only got as far as the metal pam conducting heat energy, but them I don't know why it is transferred through the water...?
     
  2. jcsd
  3. Jun 28, 2013 #2

    CWatters

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    What are the three ways heat can be transported? Conduction is one, what are the other two and which do you think is likely to occur and where?
     
  4. Jun 28, 2013 #3
    Convection and radiation? Radiation would occur to boil the water wouldn't it? I'm not sure about convection though...
     
  5. Jun 28, 2013 #4

    CWatters

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    Convection and radiation are the other two.

    OK here are some hints...

    1) The burning gas rises up to the pan and flows up the sides of the pan due to....??

    2) The heat is conducted through the walls of the pan into the water. (You already got that).

    3) The layer of water on the bottom of the pan is heated first. Soon it is hotter than rest of the water so...??
     
  6. Jun 28, 2013 #5
    Is the first convection and third radiation?
     
  7. Jun 28, 2013 #6
    ...as radiation gives the particles of the food more energy, so they vibrate faster and produce heat which heats the food?
     
  8. Jun 28, 2013 #7

    CWatters

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    Sorry but 1 and 3 are both convection.

    Inside the space station where there is no gravity a candle flame is spherical because there is no convection. On earth the hot flame cause the burnt gas and air to rise by convection.

    Inside the pan the water on the bottom is heated first by conduction so it becomes less dense than the rest of the water and convection is triggered. The hot water rises and is replaced by colder water which sinks and is heated in turn by conduction. You can see the water moving in this vid with the aid of some die..



    With an electric ring you would get a mixture of conduction and radiation between the red hot ring and the bottom of the pan although I'm not sure what proportion of the heat flows by each method.
     
    Last edited by a moderator: Sep 25, 2014
  9. Jun 28, 2013 #8
    Oooh ok! I'm with you!! Apologies, I haven't actually studied this so I'm working from scratch! Always helpful when you get set work you've been taught nothing about...
     
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