sunlight

[krishnamachary]

why shining material is hot when it is kept to the sunlight

[DrP]

13 minutes ago, krishnamachary said:

why shining material is hot when it is kept to the sunlight

Which material? Most things get warmer when left in the sun. They absorb the suns rays and warm up. I think the type of material is more important than how shiny it is, but the more reflective/shiny the surface the less energy it would absorb as some would be reflected.

[Strange]

So, to be explicit, a shiny object will (all other things being equal) be less hot than a matt black object.

However, a shiny object might be more likely to be made of metal than say plastic and so may feel hotter to the touch because it is a better conductor.

(I will suggest that the mods move this to Physics)

[StringJunky]

An object may be reflective to visible light but absorb heat producing wavelengths in the UV or IR range.

[DeoxyRiboRobert]

When you coat something in black paint you prevent it from reflecting visible light, whereas white materials reflect the light. This causes the black material to heat up faster, since the light absorbed by the black material must be dissipated in some form, which is heat.

Here's a useful website with a nice graphic that I used today to explain something similar, perhaps it's of some use to you:

http://www.gcsescience.com/pen10-matt-black.htm

[swansont]

The term here is emissivity, which is basically the degree to which something acts like a blackbody (perfect absorber and emitter, has emissivity of 1). As StringJunky notes, the value for real objects may be wavelength-dependent.

[StringJunky]

30 minutes ago, swansont said:

The term here is emissivity, which is basically the degree to which something acts like a blackbody (perfect absorber and emitter, has emissivity of 1). As StringJunky notes, the value for real objects may be wavelength-dependent.

A  question directly related: why are IR and UV heat-producing but the intermediate frequencies aren't, or as much? Is it because they are the wrong energies to excite electrons?

Edited December 7, 2017 by StringJunky

[swansont]

46 minutes ago, StringJunky said:

A  question directly related: why are IR and UV heat-producing but the intermediate frequencies aren't, or as much? Is it because they are the wrong energies to excite electrons?

They all heat things up. Sunlight is mostly in the visible range, and it does just fine at raising temperatures. It may be for some objects that the emissivity is lower in the visible, meaning the object reflects, in which case the other wavelengths are more effective. But unless the object is transparent, it absorbs light in the visible spectrum, and that in turn creates phonons.  

IR is often associated with heat because something at ambient to a few hundred degrees above will radiate strongly in the IR.

[StringJunky]

23 minutes ago, swansont said:

They all heat things up. Sunlight is mostly in the visible range, and it does just fine at raising temperatures. It may be for some objects that the emissivity is lower in the visible, meaning the object reflects, in which case the other wavelengths are more effective. But unless the object is transparent, it absorbs light in the visible spectrum, and that in turn creates phonons.  

IR is often associated with heat because something at ambient to a few hundred degrees above will radiate strongly in the IR.

Cheers.

[DrP]

1 hour ago, StringJunky said:

A  question directly related: why are IR and UV heat-producing but the intermediate frequencies aren't, or as much? Is it because they are the wrong energies to excite electrons?

It isn't just electrons it is molecular vibrations. The molecules absorb the light or UV or IR at the frequencies that resonate with the vibrational frequencies of the molecular bonds then the bonds vibrate harder when the energy is absorbed.

 

22 minutes ago, swansont said:

They all heat things up. Sunlight is mostly in the visible range, and it does just fine at raising temperatures. It may be for some objects that the emissivity is lower in the visible, meaning the object reflects, in which case the other wavelengths are more effective.

This is why I asked the OP 'Which material'? in replay to his question in the OP.

[StringJunky]

8 minutes ago, DrP said:

It isn't just electrons it is molecular vibrations. The molecules absorb the light or UV or IR at the frequencies that resonate with the vibrational frequencies of the molecular bonds then the bonds vibrate harder when the energy is absorbed.

That's the phonons swansont mentioned, isn't it?

[swansont]

Just now, StringJunky said:

That's the phonons swansont mentioned, isn't it?

Right.

 

[Sensei]

3 hours ago, StringJunky said:

A  question directly related: why are IR and UV heat-producing but the intermediate frequencies aren't, or as much? Is it because they are the wrong energies to excite electrons?

Actually early XIX century scientists split light using prism and placed couple thermometers at different colors of rainbow.

They noticed that different colors of rainbow increased temperature by different amount. That's how IR was discovered- William Herschel placed thermometer in area of spectrum where was no visible light.

 

"The discovery of infrared radiation is ascribed to William Herschel, the astronomer, in the early 19th century. Herschel published his results in 1800 before the Royal Society of London. Herschel used a prism to refract light from the sun and detected the infrared, beyond the red part of the spectrum, through an increase in the temperature recorded on a thermometer. "

https://en.wikipedia.org/wiki/Infrared

 

[StringJunky]

6 minutes ago, Sensei said:

Actually early XIX century scientists split light using prism and placed couple thermometers at different colors of rainbow.

They noticed that different colors of rainbow increased temperature by different amount. That's how IR was discovered- William Herschel placed thermometer in area of spectrum where was no visible light.

 

"The discovery of infrared radiation is ascribed to William Herschel, the astronomer, in the early 19th century. Herschel published his results in 1800 before the Royal Society of London. Herschel used a prism to refract light from the sun and detected the infrared, beyond the red part of the spectrum, through an increase in the temperature recorded on a thermometer. "

https://en.wikipedia.org/wiki/Infrared

 

Interesting. That would a good school experiment for kids of the appropriate age.

[DrP]

31 minutes ago, StringJunky said:

Interesting. That would a good school experiment for kids of the appropriate age.

I think we did the one with black and white polystyrene cups with water in them with a thermometer back in junior school or very early secondary. Obviously, the water in the black matt cups got warmer quicker than the shiny white ones when left in the sun...   hmm...  have I remembered this correctly???  :-/   did we do it or did we watch a video about it?  One or the other.  

[StringJunky]

25 minutes ago, DrP said:

I think we did the one with black and white polystyrene cups with water in them with a thermometer back in junior school or very early secondary. Obviously, the water in the black matt cups got warmer quicker than the shiny white ones when left in the sun...   hmm...  have I remembered this correctly???  :-/   did we do it or did we watch a video about it?  One or the other.  

Yes.   With the Herschel experiment though you can pick out the invisible parts with a thermometer

[swansont]

24 minutes ago, StringJunky said:

Yes.   With the Herschel experiment though you can pick out the invisible parts with a thermometer

That experiment would probably work even better with an incandescent light bulb as a source, because it has even more of its spectrum in the NIR and the atmosphere hasn't filtered any out .

[StringJunky]

Just now, swansont said:

That experiment would probably work even better with an incandescent light bulb as a source, because it has even more of its spectrum in the IR and the atmosphere hasn't filtered any out .

Yes, true, and more portable

[Sensei]

1 hour ago, DrP said:

I think we did the one with black and white polystyrene cups with water in them with a thermometer back in junior school or very early secondary. Obviously, the water in the black matt cups got warmer quicker than the shiny white ones when left in the sun...   hmm...  have I remembered this correctly???  :-/   did we do it or did we watch a video about it?  One or the other.  

Looks to me like different experiment- checking whether white material reflects light and black material absorbs light (therefore increase of the temperature).

ps. Nevertheless, worth showing to kids.

 

Edited December 7, 2017 by Sensei

[John Cuthber]

4 hours ago, StringJunky said:

Yes, true, and more portable

Yes, it's a dratted nuisance having to carry the sun round with you.

[J.C.MacSwell]

1 hour ago, John Cuthber said:

Yes, it's a dratted nuisance having to carry the sun round with you.

That's not just money burning a hole in your pocket....