Why Does Wet Paper Allow More Light to Pass Through?

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Discussion Overview

The discussion centers around the optical properties of wet versus dry paper, specifically why wet paper allows more light to pass through. It includes theoretical explanations and observations related to light scattering and surface interactions.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification

Main Points Raised

  • One participant suggests that the increased transparency of wet paper is due to water reducing surface irregularities, making the surface smoother and thus reducing reflection.
  • Another participant mentions that using an organic solvent with a refractive index matching that of the paper can make it transparent enough to read through without opening an envelope.
  • A different viewpoint emphasizes that the reduced scattering in wet paper is a result of the change in the relative refractive indices of paper and air compared to paper and water, leading to lower scattering.

Areas of Agreement / Disagreement

Participants present multiple explanations for the phenomenon, indicating that there is no consensus on a single definitive reason for why wet paper allows more light to pass through.

Contextual Notes

The discussion involves assumptions about the properties of materials and their interactions with light, which may depend on specific conditions such as the type of solvent used and the nature of the paper.

vin300
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Why does a wet piece of paper let through more light than a dry one?
 
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Most of the change in transparency of paper [and tee shirts] to allow more light thru when wet is probably because the water reduces the surface irregularities by holding them together, flatter, reducing reflection...it makes the surface 'smoother'.


Diffuse reflection - Generally, when light strikes the surface of a (non-metallic and non-glassy) solid material, it bounces off in all directions due to multiple reflections by the microscopic irregularities inside the material ... and by its surface, if it is rough.

More here:
http://en.wikipedia.org/wiki/Translucent#Light_scattering_in_solids
 
Yes. In fact, if you wet it with an organic solvent whose index matches that of the paper, it will become transparent and allow you to read the letter inside an envelope without opening it.
 
vin300 said:
Why does a wet piece of paper let through more light than a dry one?

Because there is reduced scattering, due to the change in relative refractive indices of paper/air vs. paper water. Lower Δn, less scattering.
 
Thanks.That helped.
 

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