# Tag Info

0

$E\left(\lambda\right)$ is the energy of one photon of light with wavelength $\lambda$ $f\left(E\left(\lambda\right)\right)$ is the number of photons in a state with wavelength $\lambda$ $D\left(\lambda\right)d\lambda$ is the number of states with wavelengths between $\lambda$ and $\lambda+d\lambda$. ($D\left(\lambda\right)$ is the density of states.) ...

1

I'm assuming that this section of the book is talking about the ultraviolet catastrophe, where an ideal black body in thermal equilibrium will emit an infinite amount of power through radiative means. The source goes on to say: The ultraviolet catastrophe results from the equipartition theorem of classical statistical mechanics which states that all ...

2

Any warm body radiates electromagnetic radiation with a spectrum that depends on the temperature. Above 500 degree centrigrade there is enough radiation in the visible part of the spectrum to be visible but at lower temperatures most of the radiation is at infrared frequencies or lower. Our eyes are not sensitive to infrared radiation so we do not see it.

4

The human eye is only capable of perceiving a very limited range of electromagnetic radiation, with wavelengths ~400-800 nanometer. Objects at low temperatures (room temperature) do not emit an appreciable amount of radiation in this range. The fact that we CAN see objects when it's light is due to reflection. For more info, take a look at this wikipedia ...

3

Cold bodies radiate mostly in the infrared zone (invisible to the human eye), but as the temperature increases the body will emmit higher frequencies with more intensity. So room temperature obects will not be seen due to black body radiation. As you can see, hot bodies are visible because they emmit visible light mostly.

2

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 ...

1

The Earth radiates heat as well as absorbing it from the Sun. At any given time, it does not radiate exactly as much heat as it absorbs, since the difference can be accounted for in changes in its internal energy (climate shifts etc.), as well as in sources of heat here on earth (geothermal and manmade energy).

3

The sun's spectrum is very complex, and indeed there are a lot of "lines" both light and dark (emission and absorption) amidst a sea of what looks to be continuous frequencies. Note that the atoms you study in a textbook are idealizations. In a hot object such as the sun, some photons come to us by way of atomic emissions, but the speeds of the atoms that ...

-3

Certain wavelengths of electromagnetic spectrum is emitted when the electrons in an atom to move from a higher level to a lower. The wavelength that is emitted depends upon the number of shells the electrons move down. When an electron/electrons move into certain number shells, white light is emitted i.e. when two hydrogen atoms fuse into an Helium atom, ...

0

Only electrons confined to a bounded phase space have a discrete spectrum. The electrons you are imagining are somehow already "in orbit", and, in that case, I would agree with you, but an electron that is coming in on an otherwise hyperbolic trajectory (asymptotically speaking) that happens to pass too close will probably be captured, so there is a ...

0

I wouldn't say it is a myth. Like you say, it's complicated. When you are in the sun, the predominant source of heating is from incident radiation, whereas in the shade cooling would take place primarily through convection, conduction and evaporation. When you are in the shade, you are just not that hot compared to your surroundings for radiative cooling to ...

4

The answers posted so far are correct but miss the questioner's point. Planck originally (and incorrectly) attempted to derive the law of black-body radiation by assuming that energy was an infinitely divisible "fluid" which could be apportioned smoothly into a large collection of containers (i.e., the resonators - molecules - in the walls of the black-body ...

0

But this is for perfect blackbodies only, which have no theoretical existence. Just for clarification, the Wien displacement law is not valid for emission spectrum "of blackbodies only". It is valid for any radiation in thermodynamic equilibrium with matter (equilibrium radiation), which is a more general concept that does not require presence of any ...

Top 50 recent answers are included