Color of Objects: Questions Answered by ledamage

[ledamage]

Hi there!

Everyone knows that the color of certain objects is due to their capability to absorb and to reflect light at certain wavelengths which has to do with the distance between the atomic or molecular energy levels. But I still have two stupid questions.

1. Consider ordinary objects like a table or a chair (but not glass). If it is hit by light at a wavelength where there is no resonant atomic or molecular transition, why does it scatter the light instead of letting it pass through?

2. What happens with the absorbed energy (stored in the excited atoms, molecules etc.)? Obviously, it is not re-emitted since otherwise everything was white...ledamage

 

[malawi_glenn]

It both scatters and let light passing through it, and you have thus enteried "Photon interaction with matter", such as compton scattering and pair production, and the good ol' exponential decay law.

Yes, atoms get exciited, excite plasomos, ionize atoms etc.

 

[mgb_phys]

1. Consider ordinary objects like a table or a chair (but not glass). If it is hit by light at a wavelength where there is no resonant atomic or molecular transition, why does it scatter the light instead of letting it pass through?

Transparent/scattering is more similar than you would think. It's just that in a glass or a crystal the arrangement of atoms causes the light to 'scatter' in the same direction - ie go straight through. ( I know this isn't the TECHNICAL definition of scatter).

2. What happens with the absorbed energy (stored in the excited atoms, molecules etc.)? Obviously, it is not re-emitted since otherwise everything was white...

It goes into heat. Put a black object and a white/reflective object out in the sun and you can see where the energy goes.

 

[malawi_glenn]

And the heat is due to vibration motion.

 

[cesiumfrog]

2. To emphasise, most of the light absorbed by the chair will go into microscopic vibrations of the "lattice", rather than exciting specific atoms or molecules (and so a continuous spectrum of colours can be absorbed).

1. Even if a material does not absorb light, it can still interact with (scatter) that light. For example, the passing electric wave causes an atom's electron cloud to oscillate up and down (without being excited to a higher energy level), producing secondary EM waves that interfere to scatter/reflect/refract the light.

(And part of the reason the chair looks so different to glass is often just that the chair has a much more irregular surface on a small scale. This is why clouds, paper and cotton look different to shallow water, greasy paper and wet t-shirts.).

 

[ledamage]

Thanks to you all!