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The Mystery of The Stove Top Heating Element

  1. Dec 26, 2011 #1
    This has been bugging me and I just can't seem to figure out a solid answer.

    My electric stove has different sized heating elements where the size comes from just a longer heating element. It looks like this:

    http://www.sausagemaker.com/ProductImages/41516.jpg [Broken]

    When I measure the resistance of the small one I get ~45 Ohms, whereas, the longer one has ~26 Ohms.

    Intuitively, you would think the longer coil would have more resistance so I'm trying to understand why this isn't the case.

    My current two theories are: (1) a different concentration of doping materials are being used (which doesn't seem like a very efficient manufacturing process) or (2) the diameters are different inside the black coating (which doesn't seem right either).

    Anyone know the answer or have another idea?
     
    Last edited by a moderator: May 5, 2017
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  3. Dec 26, 2011 #2

    rcgldr

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    My guess is the longer element is designed to have lower resistance in order to consume more power and generate more heat. I don't know if the design for both elements ends up consuming the same fixed amount of power per unit length of element.
     
  4. Dec 26, 2011 #3

    Yeah, I was thinking along the same lines. But was wondering what really is different about the two heating elements that gives it that property (e.g. different material or different cross-sectional areas)
     
  5. Dec 26, 2011 #4

    AlephZero

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    The electrical resistance is a wire coiled in a helix inside the "tube" that you can see. The higher resistance element will probably use thinner wire with a higher resistance per unit length.

    The power (heat) produced = V2/R and V is fixed by the mains electricity supply, so a bigger value of R gives less heat generated.
     
  6. Dec 26, 2011 #5

    rcgldr

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    The heating elements are wires wrapped in an eletrcial insulator that conducts the heat. Can you see a difference in the wire diameters? Perhaps a different compound is used in the wires. I tried a web search, but didn't have any luck finiding resistance numbers, other than they tend to range from 20 to 120 ohms.
     
  7. Dec 26, 2011 #6
    So you think it's a geometric not material difference? That would go along with my second theory.

    I am really close to cutting the heating element in half haha....oh the things that get me side tracked.
     
  8. Dec 26, 2011 #7
  9. Dec 26, 2011 #8

    AlephZero

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    It you can see the wires, you have a big safety problem!!! Remember these elements are designed so that accidentally pouring a pan full of salty water over them while they are switched on won't electrocute you.
     
  10. Dec 26, 2011 #9

    rcgldr

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    In the image shown in the OP, you can see wires protuding from the ends of the burner element.
     
  11. Dec 26, 2011 #10

    AlephZero

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    Oops, I didn't look that closely at the picture. The elements I'm familiar with have a watertight plug and socket connection system, not bare wires.
     
  12. Dec 27, 2011 #11
    Those are almost certainly not the heating elements, just wires for making electrical connections. There's no reason to be producing heat there and good reasons to make the connections to the actual heating element in the factory and keep them well protected inside the tube.
     
  13. Dec 27, 2011 #12

    sophiecentaur

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    The length that has been chosen for the coiled up element (the big thing you can see) is probably based on the temperature that it is designed to reach. Even with a low power element, you may want it to reach red heat. I have a feeling that, if you had a long coil, it would not actually get that hot because of natural heat loss and energy balance. Hence they make the low power elements shorter so that they can still reach a high temperature and radiate their heat to the pan.
    This has nothing to do with the way they achieve the actual resistance of the nichrome wire inside. This is done by choosing the gauge of wire and the length that is coiled up inside.
     
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