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

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Discussion Overview

The discussion explores the interactions between light and black surfaces, particularly focusing on absorption, reflection, and transmission of light. Participants inquire about the micro-scale effects of shining light on black surfaces, the comparison with transparent materials like glass, and the underlying physics of these phenomena.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Some participants wonder if all photons are absorbed by a black surface and what happens to the energy, questioning if it converts to thermal energy.
  • There is a comparison made between black surfaces and transparent materials, with some participants asserting that both do not reflect light, leading to confusion about their properties.
  • Participants discuss the differences between absorption, reflection, scattering, and transmission, emphasizing that a black object absorbs all light while a transparent object transmits it.
  • One participant raises a question about the conditions under which light is reflected, particularly in relation to the band gap of materials, and inquires why both silver and diamond reflect light despite their differing band gap properties.
  • Another participant questions the reflection properties of different materials, such as graphite compared to copper or silver, attributing differences to atomic bonding and absorption characteristics.

Areas of Agreement / Disagreement

Participants express differing views on the properties of black surfaces versus transparent materials, with some confusion remaining about the definitions and behaviors of these materials. There is no consensus on the specifics of light interaction with various surfaces.

Contextual Notes

Participants mention concepts like band gaps and atomic bonding, but these ideas are not fully resolved or agreed upon, indicating a need for further clarification on these topics.

Maxwells Demon
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?
 
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Zz.
 
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..
 
Maxwells Demon said:
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.
 
No. Light can do three things when hitting an object: be absorbed, be reflected, or be transmitted. Something black absorbs all light.
 
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.
 
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 won't 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.
 
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Maxwells Demon said:
want to tell about the difference? Or else I won't learn :P
:confused: :confused: Transmission is what glass does. It let's light pass through without reflecting or absorbing it.
 
  • #10
haiha said:
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).
 
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  • #11
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?
 
  • #12
haiha said:
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.
 

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