5 votes

Why spontaneous emission?

If stimulated emission was the only radiative emission process then objects in thermal equilibrium would be transparent. Any absorption of a light beam would be exactly balanced by stimulated emission ...
  • 114k
2 votes

Black Body Radiation and Tungsten Filament?

light bulbs are usually designed so that the bulb temperature is below the ignition point for paper, which is about 450 F. The intensity of the filament output drops with distance from the filament ...
2 votes

Black Body Radiation and Tungsten Filament?

It's possible that the camera is not able to resolve the filament. If a pixel in the detector (at the image) corresponds to a larger width than the filament (at the object), the camera will estimate a ...
  • 804
2 votes

What physical property defines how fast a material loses thermal energy?

It’s still thermal conductivity. For thermal energy to travel there must be a temperature gradient. This is true for dissipating thermal energy as well. How long it takes to heat the oil will depend ...
  • 41
2 votes
Accepted

How does apparent brightness (or stellar magnitude) change with distance in an expanding universe

There are two separate issues here, the inverse-square law and redshift. Inverse-square law: the total power received from an object decreases as $r^2$, but also the area over which it's spread ...
  • 19.4k
1 vote

What physical property defines how fast a material loses thermal energy?

Pre-EDIT: As I go to post this, I see that a better and quite well-constructed answer by @rddr has already been posted (above, no doubt) while I was writing. Nonetheless I will leave this here along ...
  • 11
1 vote

Will a black hole disappear?

We cannot be sure yet if a Black Hole fully evaporates into "nothing" or leaves a stable quantum remnant. Hawking Radiation is hard to observe because it is an incredibly slow process for ...
1 vote

How do we determine the color of heated glass?

The spectral emissivity, $e_{\lambda}$, of a surface is the power it emits in a narrow band of wavelengths centred on $\lambda$, expressed as a fraction of the power emitted by a black body of the ...
1 vote

Can we concentrate the "cold of the sky" with a parabolic dish to cool things down during the day?

Take an object such as a slab of aluminium and expose it to a cloudless night sky. The upper surface will radiate heat to space. Now position a parabolic reflector under the slab such that the slab is ...

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