Physics Help Forum How mirror reflects light in atomic levels?

 Light and Optics Light and Optics Physics Help Forum

 Sep 28th 2014, 12:29 AM #1 Member   Join Date: Mar 2013 Posts: 37 How mirror reflects light in atomic levels? Light hits green leaf, we see green light, because green pigment within leaf repel each other, so green light would be reflected, and we see green leaf. Is it corrected concept? Carbon is black, because most of visible wavelengths are absorbed into carbon atom, and nothing is reflected, so we see black carbon. On the other words, carbon absorbs energy with certain wavelength. In term of efficiency of reflection, the less energy to be absorbed from objects, the higher efficiency of reflection the object is, would it be correct? I would like to know on what make mirror absorbing less energy from light comparing to carbon, so we can see clear image with most of light wavelength from reflection ... Does anyone have any suggestions? Thanks in advance for any suggestions Last edited by oem7110; Sep 28th 2014 at 12:36 AM.
Sep 30th 2014, 09:39 AM   #2
Physics Team

Join Date: Jun 2010
Location: Morristown, NJ USA
Posts: 2,352
 Originally Posted by oem7110 Light hits green leaf, we see green light, because green pigment within leaf repel each other, so green light would be reflected, and we see green leaf. Is it corrected concept?
Not quite. The leaf appears green because it has absorbed most of the red in sun light, leaving yellow and blue to be reflected back. Combine yellow and blue and it appears green to our eyes.

 Originally Posted by oem7110 Carbon is black, because most of visible wavelengths are absorbed into carbon atom, and nothing is reflected, so we see black carbon. On the other words, carbon absorbs energy with certain wavelength.
Yes.

 Originally Posted by oem7110 In term of efficiency of reflection, the less energy to be absorbed from objects, the higher efficiency of reflection the object is, would it be correct?
You're almost right, but are ignoring transmission of light. When light hits a surface three things are possible: absorption, reflection, or transmission. Think of light hitting a window - it is transmitted through, so the window neither absorbs nor reflects.

 Originally Posted by oem7110 I would like to know on what make mirror absorbing less energy from light comparing to carbon, so we can see clear image with most of light wavelength from reflection ...
Carbon appears black because it absorbs visible light very efficiently. When a photon of visible light hits an atom of carbon the electrons in the carbon absorb the energy and are kicked into a higher energy level. When the electron's energy level decays to a lower state a photon is emitted, but that photon has a different wavelength than visible light, such as infrared, so we can't see it. On the other hand an object that appears white to us re-emits photons across the visible spectrum. Now, as for why a mirror has perfect reflection (i.e. angle of incidence = angle of reflection) - it's a bit difficult to explain using quantum electrodynamic theory of photons - much easier to think of light as a wave to understand how reflection works.

Sep 30th 2014, 10:03 AM   #3
Member

Join Date: Mar 2013
Posts: 37
 Originally Posted by ChipB When a photon of visible light hits an atom of carbon the electrons in the carbon absorb the energy and are kicked into a higher energy level. When the electron's energy level decays to a lower state a photon is emitted, but that photon has a different wavelength than visible light, such as infrared, so we can't see it. On the other hand an object that appears white to us re-emits photons across the visible spectrum. Now, as for why a mirror has perfect reflection (i.e. angle of incidence = angle of reflection) - it's a bit difficult to explain using quantum electrodynamic theory of photons - much easier to think of light as a wave to understand how reflection works.
I don't understand clearly on how the process of decays work to emit a photon of light of the same wavelength.

A mirror is 100% reflective, it is made of high polished aluminium.

When light hits atom, it would transfer energy and raise the energy levels of electron within atom, aluminium is better conductivity than wood, so how do those decayed energy to be handled differently between aluminium (Mirror) and wood (Carbon)? Referring to following statements, for the decayed process, I would like to know on how aluminium rapidly discharge those current related to emit a photon of light of the same wavelength.

 Above the Fermi level, energy levels are empty (empty at absolute zero), and can accept excited electrons. The surface of a metal can absorb all wavelengths of incident light, and excited electrons jump to a higher unoccupied energy level. This creates current, which rapidly discharges to emit a photon of light of the same wavelength. So, most of the incident light is immediately re-emitted at the surface, creating the metallic luster we see in gold, silver, copper, and other metals. This is why most metals are white or silver, and a smooth surface will be highly reflective, since it does not allow light to penetrate deeply.
Source :
http://www.webexhibits.org/causesofcolor/9.html

 Originally Posted by ChipB The leaf appears green because it has absorbed most of the red in sun light, leaving yellow and blue to be reflected back. Combine yellow and blue and it appears green to our eyes.
On the other hands, for a green leaf, when leaf absorbed most of the red in sun light, those energy from red wavelength is absorbed and electrons are kicked into a higher energy level, but yellow and blue wavelength are not absorbed, I would like to know on what object makes this decision on selecting certain wavelength to be absorbed, and how does this process work in atomic levels?

Do you have any suggestions?
Thanks you very much for any suggestions :>

 Tags atomic, levels, light, mirror, reflects