Tag Info

0

In general, the limit of $T \rightarrow \infty$ is not as straightforward, because at some point the particles move so fast that we need to account for relativistic effects. We often regard the Planck temperature of $T_\text{P} \approx 1.4 \cdot 10^{32}\,\text{K}$ as the hottest possible, according to our current understanding of the universe. A body with ...

1

To Malawby: ALL radiation hitting the earth is either absorbed or reflected. Regardless of temperature of the source or the earth. What happen in this scenario is that the earth and the green gasses are exchanging energy by radiation with the net effect of 0 W/m2. If the earth was warmer we would have a net effect of >0 W/m2 etc to the green gasses. Even ...

0

Great question! So the solar constant at the Earth's position is 1370 $W/m^2$. The Earth, of course, can to a good degree, be modeled as a sphere. But the cross sectional area presented to the Sun is that of a circle. The area of a circle is, of course, $\pi R^2$, where R would be the radius of the Earth. So the total solar radiation captured is: 1370*...

0

You may buy a diffraction grating for telescopic use, look for Star Analyzer. They can be placed in front of a telephoto lens and gives spectra of the sun and stars. For the sun it may be necessary to dampen the light.

0

what you need is a spectrometer, which can be made out of pieces of cardboard and a strip of clear plastic film with tiny scratches in it called a diffraction grating. There are cheap do-it-yourself spectrometer kits available on-line for students to build their own spectrometers in the classroom, and they come with instructions on how to use them and what ...

1

1} For the absorption spectrum, you have to shine a light through the gas. Light usually comes from one direction. Hydrogen will absorb specific wavelengths from that light and get promoted to an excited state. It will then return to the ground state and emit that light in all directions. So if you look at the light shining through the gas, you see the ...

2

Wein's displacement law has to do with how the peak in a blackbody spectrum shifts with temperature. It does not have anything to do with whether a particular temperature is required for a substance to absorb or radiate at that wavelength. Carbon dioxide will both absorb and radiate at 15 $\mu$m in the both troposphere and stratosphere. If radiation at the ...

1

You are quite right that it is thermodynamically impossible to heat something hotter than the surface of the sun using only sunlight and passive optical elements (such as a filter that would block some wavelengths). Heat would then be spontaneously flowing from somewhere less hot to somewhere hotter, and that doesn’t happen. The roadblocks you will encounter ...

-1

No, the truncated spectra is not a different type of Black-body radiation. (Please look at the spectras of different temperatures.) As @boyfarrell suggests, if you truncate the incoming spectra, the overall energy absorbtion will be lover. (The integrated radiance will be lower, because you integrate over a limited frequency range.) Note: At first glance ...

0

There is some research that shows that curly hair keeps the head cooler in warmer climates. https://daily.jstor.org/why-do-some-people-have-curly-hair-and-others-straight/ Whereas straight hair keeps the head warmer. I would say this matches an observation that ethnicities primarily found in colder climates tend to have straight hair.

0

0 I think its a really good question, and I didn't see it answered as I would have liked if I had asked it. I am not sure I can answer it better, but here is my input. A cavity with a hole will only emit through that hole such radiation as is caused by the thermal energy of material from which the cavity is made. That is, if the hole and the environment are ...

0

Which brings me to my question: How is this possible, and what is the lowest temperature one can hope to cool a well insulated object during night? It is possible due to what's called radiative sky cooling. https://www.popularmechanics.com/technology/infrastructure/a29036147/radiative-sky-cooling/ To quote from the link: “This effect occurs naturally all ...

1

Let's model this as a thermodynamic system with three components: the water, the air, and outer space (a fourth component would be the ground, but we'll assume the insulation between the water and the ground below it is very good, and leave it out). For simplicity, let's pretend that the air is perfectly transparent to the infrared frequencies at which the ...

0

At least in the US, devices that are designed to by continuously used are allowed to use only 1500 W cite. So most space heaters are designed to use 1500 W. Assuming that the manufacturers design the heaters to compensate for different resistance, they will remain at 1500 W regardless of the temperature of the coils.

0

John Murphy simply asserts that "fluxes cannot be added." He doesn't explain why, if you have two energy sources, they're not both imparting energy. Suffice to say that in real life, the greenhouse effect does not violate the second law of thermodynamics, and that one should get one's science from scientists and not from internet crackpots. https:...

1

Power = $I^2 R$ and $V = IR$ so power = $V^2 / R$. A simple device like this probably works at constant $V$ rather than constant $I$, so the power goes up when the resistance goes down. The net result is therefore more generation of heat per unit time. If that is what you want then you have achieved it (and your electricity bill will furnish the cost).

3

Metal resistive coils in the space heaters (and other heater appliances like water heaters) are made of alloys that have more or less constant resistance over their full operating temperature range. That's why one generally doesn't get measurable increase in the heat output by cooling them. The total heat output will be increased with the amount of energy ...

15

If your fan cools the electric coils, their resistance will go down and the current flowing through them will go up, and so will the wattage output of the heater. By the way, the fan inside the heater housing is the primary thing moving the heat off the coils. The fan you set up behind it is mostly moving that heat to distant parts of the room in which it is ...

9

The sensation of something feeling "hot" is a function of the rate of heat transfer to the skin and the duration of the transfer. The product of the rate and duration of heat transfer is the amount of heat transferred to the skin. The rate of heat transfer of the aluminum foil, being a metal, is relatively high because of its high thermal ...

3

The foil is so thin that it loses its heat energy very quickly. Even though it may initially be as hot or hotter than the pizza when removed from the oven, its heat will cool very quickly. When you touch it, it reaches thermal equilibrium with your skin before it can heat your skin enough to burn you.

2

The revolutionary insight here is precisely that the prediction from classical electrodynamics - which would suggest that the allowed energies for each mode are continuous - is wrong. If you instead restrict the allowed energies to discrete multiples of $h\nu$ (where $\nu$ is the frequency of the mode in question and $h$ is some constant), then the ...

1

Can we model the hydrogen gas present in space as an ideal gas? One of the criteria for an ideal gas is the molecules need to be far enough apart so that intermolecular forces can be ignored. Certainly in space between stars and planets any hydrogen molecules would be far enough apart to consider the gas ideal. What's more, in the atmospheres of stars and ...

Top 50 recent answers are included