# What happens when you shine a light on a black surface?

Maxwells Demon

## Main Question or Discussion Point

1. I just wondered what happens on micro scale when you shine a light on a black surface.. Since you see it, does all the photons get absorbed? If they do what happens to the energy, does it convert to thermal energy?

2. If black doesn't reflect any photons, then we should see nothing. But what about a perfect transparent piece of glass, that doesn't reflect any photons either does it?

3. If you put to objects in the sun, a white and a black, the black becomes hotter because it absorbs the light. Can someone explain more deeply what really goes on?

Related Other Physics Topics News on Phys.org
ZapperZ
Staff Emeritus

Zz.

Maxwells Demon
about the one with the glass.. a thing that doesn't reflect light is black.. so something black and a piece of glass is essentially the same thing right..? or?

ZapperZ I'll do it right away..

about the one with the glass.. a thing that doesn't reflect light is black.. so something black and a piece of glass is essentially the same thing right..? or?

ZapperZ I'll do it right away..
No, a piece of glass and something black is not the same. Not even in this particular context. There is a distinct difference from absorption, reflection, scattering and transmission.

russ_watters
Mentor
No. Light can do three things when hitting an object: be absorbed, be reflected, or be transmitted. Something black absorbs all light.

ZapperZ
Staff Emeritus
Except that in the similar case of there being no "perfect" reflector, there is also not a whole lot of perfect "black" surfaces, discounting blackbody cavities and "blackholes".

Zz.

Maxwells Demon
No, a piece of glass and something black is not the same. Not even in this particular context. There is a distinct difference from absorption, reflection, scattering and transmission.

want to tell about the difference? Or else I wont learn :P

In reading this topic, I just think of a question . As I know, and hope it is correct, the light transmits through a material when its quantum energy is lower than the material band gap, and it is absorbed if the energy is larger than the band gap . So in case the light reflects, what is the reason for that?.
Why both silver and diamond reflect light very well when silver has no band gap and diamond has very large one

Thanks.

Last edited:
russ_watters
Mentor
want to tell about the difference? Or else I wont learn :P
Transmission is what glass does. It lets light pass through without reflecting or absorbing it.

russ_watters
Mentor
Why both silver and diamond reflect light very well when silver has no band gap and diamond has very large one
Diamonds are highly transparent (not reflective). Gem diamonds reflect a little bit of light due to the facets (probably some total internal reflection going on too).

Last edited:
So, what makes the reflection property of a material?. Why a piece of graphit is not as shiny as a piece of copper of silver?

DaveC426913
Gold Member
So, what makes the reflection property of a material?. Why a piece of graphit is not as shiny as a piece of copper of silver?
Graphite has atoms very loosely bonded together (that's why it makes a good lubricant) those loose bonds will absorb virtually any frequency of photon, so no photons reflect or transmit.