Thermal radiation in transparent objects

[dRic2]

Every objects emit thermal radiation. Now consider this case: Sun emits waves in a certian electromagneic spectrum (UV + thermal radiation + ecc...); glass is transparent to thermal radiation that usually reach Earth's surface. UV and other radiations are mainly absorbed by Ozone and other gasses in the atmosphere thus (in a hypotetical scenario) Sun can not transmit energy to glass. SO the piece of glass, which is emitting energy, should be lowering his temperature. It is obviusly not possible, but what did I miss?

 

[haruspex]

Every objects emit thermal radiation. Now consider this case: Sun emits waves in a certian electromagneic spectrum (UV + thermal radiation + ecc...); glass is transparent to thermal radiation that usually reach Earth's surface. UV and other radiations are mainly absorbed by Ozone and other gasses in the atmosphere thus (in a hypotetical scenario) Sun can not transmit energy to glass. SO the piece of glass, which is emitting energy, should be lowering his temperature. It is obviusly not possible, but what did I miss?

If an object can radiate at a certain wavelength then equally it can absorb at that wavelength.
My understanding is that most glass does absorb IR quite well, but not equally across the IR band.

 

[dRic2]

Ok but if an object A emits radiations F and G (let's call them that way to make it simple) and I place two objects (B and C) in front of him such as B absord F and is transparent to G and C is trasparent to G, how can the radiations of A reach the object C? I think it can not. But C is emetting too so it may get cooler (nonsense).

 

[haruspex]

Ok but if an object A emits radiations F and G (let's call them that way to make it simple) and I place two objects (B and C) in front of him such as B absord F and is transparent to G and C is trasparent to G, how can the radiations of A reach the object C? I think it can not. But C is emetting too so it may get cooler (nonsense).

Why is it nonsense? If the system has not reached equilibrium then C can cool.
Here's a simpler example: object A only emits/absorbs in band a, the enclosing shell B only emits/absorbs in the disjoint band b. If there is no conduction then each behaves as though the other does not exist. The equilibrium temperature of A will depend on the background radiation in band a beyond the shell.

 

[Dale]

Every objects emit thermal radiation.

Careful here. A piece of glass is NOT a black body. It will not emit as efficiently as a black body at the same temperature.

A black body is an ideal absorber, but it is also a perfect emitter. Any gray body or white body will both absorb and emit less completely.

 

[dRic2]

Careful here. A piece of glass is NOT a black body. It will not emit as efficiently as a black body at the same temperature.

A black body is an ideal absorber, but it is also a perfect emitter. Any gray body or white body will both absorb and emit less completely.

Yeah, but There is no need for this here I think.

Why is it nonsense? If the system has not reached equilibrium then C can cool.
Here's a simpler example: object A only emits/absorbs in band a, the enclosing shell B only emits/absorbs in the disjoint band b. If there is no conduction then each behaves as though the other does not exist. The equilibrium temperature of A will depend on the background radiation in band a beyond the shell.

Yes, you're right, I was Just thinking a very strange complicated thing (that I won't explain because It would be very hard) but I realized It is not possibile, so now everything fits in place