When I’m making coffee on an electric stove, why the burner with time becomes red everywhere, but not underneath the coffee pot?

When I’m making coffee on an electric stove, why the burner with time becomes red everywhere, but not underneath the coffee pot?

You can check the answer of the people under the question at Quora “make coffee on the stove

0 thoughts on “When I’m making coffee on an electric stove, why the burner with time becomes red everywhere, but not underneath the coffee pot?”

  1. Heat is transferred to the cold water so the area under the pot is colder. Once the water has all evaporated and the temperature of the pot matches that of the heating element the pot will also glow red

    Reply
  2. Since the coffee pot has liquid water in it, the temperature near the water will be close to the boiling point of water (at most). This is considerably less than the temperature required to make the electric element glow red.
    Elsewhere the element is surrounded by air (a good insulator). It loses heat only …

    Reply
  3. Thanks for the A2A.
    Underneath the coffee pot, all the heat goes into the water.
    Water has an immense amount of a characteristic called heat capacity . Metal doesn’t. What this means is that it takes a lot of energy to heat up water, and it takes a long time for it to cool off afterwards. Metal both heats up and cools off faster.
    Your coffee pot is made of metal, and so is the hot plate. The hot plate heats up everywhere. Where it’s in contact with the coffee pot, the coffee pot heats up. But the coffee pot then heats the water—all the heat goes into the water, until it’s hot enough to boil.
    The rest of the hot plate gets hotter, until it starts to glow. At that point, the heat is carried away in the form of heat radiation (mostly; some of it goes into heating the surrounding air). But the part that is under the coffee pot doesn’t get as hot—the heat goes into the coffee pot, and on into the water.
    If you keep the coffee pot on, the heat will go towards making the water boil. It takes energy to turn water from a liquid into steam. When all the water has boiled off, the hot plate will start to glow also under the coffee pot. (If the coffee pot is made of, say, cast iron, it will also start to glow. Copper or aluminium are much lighter in colour, and you will most likely not see the glow.)

    Reply
  4. Because your coffee pot acts as what is known as a heat sink. That part of the burner in contact with the pot can easily get rid of the heat that the electrical current is generating and maintains a relatively low temperature. It does so by conduction. The part exposed to air can only get rid of the heat by radiating heat and its temperature will rise until that becomes a reasonable proposition. Of course the radiated heat is a waste of good electricity. It is why your stove has different size burners. Put your pot on a more fitting -smaller- burner next time.

    Reply
  5. The coffee pot is cooling the burner directly under it. The heat is being transferred by conduction from the burner, to the bottom of the pot & then to the water in the pot.

    Dunkin’

    Reply
  6. heat is only transferred where the pot is in contact with the hotplate the area of the plate not in contact will therefore not transfer heat and will rise in temperature accordingly

    Reply
  7. Immediately underneath the pot, the burner is cooler because the pot is absorbing heat from it. A glowing burner is several hundred degrees. Meanwhile air is much less dense than water and has a lower specific heat, so it doesn’t absorb heat from the burner nearly as rapidly as water. Water also has a high heat of vaporization, meaning that it absorbs a great deal of heat just to pass from liquid to vapor at the boiling temperature. So the water in the pot is removing heat from the burner much faster than the surrounding air, with the result that in the immediate vicinity of the pot, the burner is being kept nearer the boiling temperature of water.
    The effect will be obvious if the water in the pot is allowed to boil off, at which point the burner will glow red hot all over, probably destroying the pot and possibly causing a fire.

    Reply

  8. Reply
  9. The thing about using the stove (there’s not “burner” in an electric stove, it’s a “hot plate”) is to transfer heat, not to make glow it red.
    This being said, what is happening is that the heat below the coffee pot gets into the water and the water will never be hotter than 100ºC (212ºF), hence that’s the temperature of the stove under the coffee pot. Whatever heat tends to raise that temperature will be rapidly absorbed by the never hotter than 100ºC coffee.
    Around the coffee pot the history is different. As there is no “sink” for the extra heat, this heat raises the temperature of the hot plate, well beyond the red limit, and it is very hot. It’s wasted heat, and the glowing and unwanted effect, but unless all the pots are the same size, it will happen.

    Reply
  10. As stated by other answers…
    The hotplate is slightly cooler under the coffee pot because thermal energy is being removed from the hotplate, relatively quickly, via conduction into the coffee pot.
    What has not been stated yet, is that the thermal energy generated within the hotplate excite the electrons within the material it is made of. When these atoms reach a certain temperature, the excited electrons release energy in the visible spectrum. Red is the low energy end of the spectrum, so it starts glowing at the red end of the spectrum. Underneath the coffee pot, because it is slightly cooler, the red colour is still outside the visible range – it is in fact emitting infra red radiation (your skin absorbs infra red radiation and our brain tells us “I can feel the heat coming from that hot surface – DO NOT TOUCH!”
    Therefore by comparison the outer part of the hotplate appears bright but the part under the coffee pot appears darker.
    NB : It is not correct that the hotplate under the coffee pot is no hotter than 100degC, since thermal energy is being produced faster than conduction can remove the same energy. Believe me – you will get a nasty burn if you tried to touch it. There is, in fact what is called a “temperature gradient” from the hotplate, into the metal of the coffee pot and into the water. At each junction, there is a “discontinuity” (effectively a break) in the gradient – so the water may be at 100degC maximum, but the metal of the pot and the material of the hotplate can be MUCH higher.

    Reply
  11. Because the coffee pot is taking the heat away. If the bottom were insulated that wouldn’t happen, but then you wouldn’t have coffee either.

    Reply
  12. The nichrome coils in fact are glowing red-hot. Nichrome is an alloy designed for its high electrical resistance, which turns power into heat.
    The coils are darker under the coffee pot because the heat is being absorbed and so the temperature is less.

    Reply
  13. The burner is hot, but it is a little cooler under the pot because the pot is taking a lot of heat from it to heat the water. Air cools the burner also, but much much less. Air is much thinner. It therefore steals heat slower.

    Reply
  14. I assume you have an electric burner.
    The burner has to get hot. You are seeing its blackbody radiation. The heat is being transferred by conduction. The coffee pot won’t get that hot unless all the water has boiled off (water has a high specific heat). Then the coffee pot could also get hot enough to glow red if you doing turn the heat off. (I don’t know how hot the metal must get too glow).

    Reply
  15. The color (red) is indicative of temperature. The exposed part of the burner is hotter, therefore red, than the part of the burner under the coffee pot because the cooler coffee pot is absorbing the heat keeping that portion of the burner cooler and less than red hot.

    Peet’s

    Reply
  16. Picture, please!
    By the way, I think, without the pot, the very center of an electric (ceramic) stove will remain dark. Heating element is circular, and there is no heating element on the center.

    Reply
  17. I was asked to answer but the other answers I have read answer the question adequately.
    I would like to point out that what you describe doesn’t happen with induction cooktops which induce eddy currents in the pot itself so that only the metal of the pot becomes hot. Of course the pot must be made from a ferromagnetic material or have a ferromagnetic base attached to the metal it is actually made from.
    Keep in mind that the pot heats the ceramic surface of the cooktop, but once the pot is removed, the surface doesn’t continue to produce heat the way a conventional burner does, and cools down fairly rapidly.
    Unfortunately, induction cooktops are not available on stoves that have built-in ovens for reasons that should be obvious if you give it some thought.

    Reply
  18. The pot (with water in it) is conducting away the applied heat flux from the burner by thermal contact. The part of the burner with nothing on it only has the air to conduct the air away. Air is much less thermally conductive than the pot with water in it. so the burner material continues to get red as heat flux is generated within it as a function of resistive heating of the material caused by the electrical current. The current generates heat at a much faster rate than the air is able to conduct it away, so more of the burner material retains heat and its temperature is higher.

    Reply

Leave a Comment