# Tag Info

67

Short answer: The thermometer measures actual temperature (which is the same for both), while your hand measures the transfer of energy (heat), which is higher for the pot than the air. Long answer: Keyword: Thermal Conductivity The difference is a material-specific parameter called thermal conductivity. If you are in contact with some material (gas, ...

20

The two "no" answers you've already received are correct for all practical purposes. In real-world cases there can be a difference though. The difference depends on when the refrigerator decides to cycle on and cool. If the fridge cycles on a timer or based on heat energy then there will be a difference due to the added heat capacity. The outside of the ...

14

The heat loss (power) at a particular temperature is the same. So, No - the cooling needed to maintain the thing cold stays roughly the same. However, the empty fridge has lower total heat capacity. So, it will get warm faster in the absence of power. So, it is worthwhile to fill your fridge and freezer with bottle of water a few days before a big storm ...

13

Another term is thermal resistance, This is incorrect. Thermal resistance is something that prevents heat flow. It is an entirely separate concept from electrical resistance. How is contact resistance explained? To obtain very low resistance in a material like most metals, the electrons must be delocalized from the individual atoms, and free flow ...

12

Ways I can think of to export energy from a home that do not heat the interior: Light through windows Radio energy from transmitters (WiFi, cell phone, radio, power supply noise) Sound from stereo/TV Charge in batteries Hot items carried out (coffee in travel mug) Pressure in car/bike tires supplied from your pump Vented hot air from dryer, shower, oven, ...

11

No. The rate of cooling must simply match the rate of heating, and heating rate depends only on the temperature difference you want to establish and on the thermal conductivity and surface area of the walls. More stuff in the refrigerator would give it a higher heat capacity, so that it wouldn't warm up so much when the door is opened. However, it will take ...

10

Diamond dust (or dust of any other material) won't conduct heat anywhere close to as well as the solid material. At a molecular level the dust isn't in very good contact with other grains of dust. There is plenty of separation and air in between the particles that will retard heat conductivity. If you were to compress the dust so significantly that it did ...

9

I disagree with the opinion that your skin can measure heat transfer. It can only measure temperature, or to be more precise: the surface temperature of the body you are touching. Now the thermal diffusivity comes into play: When you touch a cold piece of wood (low thermal diffusivity), you transfer heat to the wood, the boundary layer of the wood warms up ...

8

You've actually identified a key area of ongoing research known as the coronal heating problem. First, let's get one thing out of the way. You ask: Or is there a type of matter with thermal conductive properties that could accomplish this? There can be no such material. Any material that passively diffuses heat from a cooler region to a warmer one ...

8

In a microwave the EMW energy is transferred to the water molecules, but, since they are in immediate contact with other molecules (as in any food), the whole volume gets heated. You will not have a two-temperature mixture.

7

It's a steady state. If there were a pressure gradient, there would be net force on the gas (ignoring gravity). There's no net force here because the air isn't accelerating. Thus the pressure is constant. The number density varies across the box inversely to the temperature so the ideal gas law holds.

6

Compare to the energy that the Earth surface receives from the sun, how much power comes from the inner melted core ? Very little. The Earth's surface emits about 503 watts per square meter (398.2 W/m2 as infrared radiation, 86.4 W/m2 as latent heat, and 18.4 W/m2 via conduction/convection), or about 260 petawatts over all of the Earth's surface ...

6

Electricity needs charges particles (or quasi-particles) to conduct. Heat can be conducted with almost any quasi-particle. Diamond is one of the best conductors of heat in existence, and it's because of phonons, ie quasi-particles of lattice vibrations, which are strong because the diamond lattice is strong.

6

The metal rod will become hotter. Only not very much for a large rod. The energy will flow from your fingers to the metal until the temperature of the metal reaches the temperature of your fingers. For a large metal object this will never happen for all practical purposes. For a small object, though, it does happen. If you pick up a dime it will ...

5

In my opinion there is no physical reason. To cook food the same energy is needed, and to burn it too. It is behavioral differences because of the form of heat: One is aware of the dangers of gas and is much more careful in turning it off on time, when food just starts to smell "singed". Electric : we may turn it off and leave the pot on the still hot ...

5

This is a very interesting question, especially considering the very recent history of scholarship on electrical contact resistance (a term first coined in 1964 by William Shockley, one of the inventors of the transistor), as well as thermal contact resistance. For the following explanation, I will use this research paper on electrical contact resistance ...

5

Without doing the analysis, I would think that a cooling system is more effective at extracting heat from a warm container than from a cold one. For a fridge, the effectiveness (or coefficient of performance) is $Eff=Q_c/W$ is the ratio of the heat removed from the cold source (the fridge) to the energy used for the purpose. It increases with the ...

5

I can't make this a comment since I don't have enough reputation. The metal box itself can absorb some of the heat (by conduction) and then give out energy in the form of electromagnetic radiation. If you want to do some real physics with such a system, you could idealize the box as a black body and continue.

5

Heat is the thermal motion of particles. Hot object's atoms vibrate more than cold object's atoms. Heat is transfered by 3 main ways: Conduction: Heat flows from hot objects to cold objects. If you have an electric stove, the heat flows from the coils to the pan. Convection: Heat flows by bulk motion of a fluid. If you heard "hot air rises" this is the ...

5

For metals there is a connection between the thermal conductivity and electric conductivity (Wiedemann–Franz law). However specific heat is not directly related. This is because electric and thermal conductivity are due to the electrons, however the specific heat is mostly due to the ion vibrations (phonons). Despite "classical" intuition electrons ...

5

In a liquid mixture such as ethanol-water, both components vaporize to some extent. If the combined vapor pressure of the two equals the external pressure, say 1 atm, the mixture will boil. The components DO NOT boil separately. Further, the composition of the vapor and the composition of the liquid will be different from each other. This is the basic ...

5

Thermal conductivity relates to the propagation of heat, whereas electrical conductivity relates to the effective propagation of electric charge. In the case of thermal conductivity, not only the electrons play a role in the conduction but also phonons or magnons contribute to it. The electrons only play a significant role in heat conductivity in metallic ...

5

Your confusion lies within your perception of natural length in the Young's modulus formula. When we say strain=$\Delta L/L$, the $L$ refers to the natural length of the rod at a given temperature. So, if the rod is not clamped, and we increase the temperature, there is no deviation from natural length at that temperature (as we can define natural length of ...

5

By conductor of heat, do you mean that it is bad at transferring heat via conduction? Or that it is just bad at transferring heat? First, a picture of the molecular structure of an oil: Conduction Oil is a liquid. Heat transfer by conduction requires strong bonds between the molecules, so that a vibration(heat) travels down the line. With liquids, this ...

4

Your first answer is the correct one. The temporal auto-correlation function (or the time correlation function) of a fluctuating quantity $A(t)$ is $$C_{AA}(\tau) = \langle A(t) A(t+\tau)\rangle$$ This is a measure of how correlated $A(t)$ is to its value at another time $t+\tau$. The Green-Kubo formula that connects a response function (the electrical ...

4

conductivity is the inverse of resistivity which is resistance times cross-section area divided by length. So measure the resistance using a micro-ohmmeter and measure the length and area using rulers and calipers.

4

Your first assumption is not really correct. The induction cooker creates an electromagnetic field with a frequency in the range of 10 kHz to 100 kHz. The coil used in the cooker looks as follows: The coil and the frequency are choosen in such a way that the field does not extend more than a few centimeters along the axis of the setup. Now when you put a ...

4

Water boils at 100° C and atmospheric pressure. If you try to boil water in a closed container, a small amount of steam will form; this will increase the pressure, and the rest of the water will not boil (unless the container bursts or leaks). This explains why water will not boil inside a plastic sac. I don't completely understand the set-up with the ...

4

Both bodies of water will heat till 100 C (as well as the vessel). Then, the outside one will start boiling by taking latent heat from the surroundings, Now, we only have heat transfer due to conduction/radiation when there is a temperature difference (or an emf, but that's irrelevant). It's mainly conduction we need to consider, anyways. Convection won't ...

4

Matter above absolute zero will radiate (electromagnetic) energy no matter what. This is due to the motion of atoms (specifically charged subatomic particles) in the energized matter. Conduction between two bodies in thermal contact is only one means of transferring energy - it is different than radiation. The earth does not need to be in contact with ...

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