When a light beam passes through an object it goes through various light matter interactions.
1. Refraction
2. Absorption
3. Remission
And these processes explain why speed of light is slower in other mediums except vaccum
More Questions:
1. How is light wave different from EM wave ? Does all EM wave have particle nature ?
1. How light pass though matter and what is the cause of velocity decrease and how does it regain speed after existing a medium ?
1. What makes a thing(solid) transparent ?
2. What makes a liquid transparent ?
3. Are all gases transparent ?
I guesses gases may not be purely transparent but extinction coefficient is so negligibly small that we can assume it as transparent.
4. Why glass is transparent? (MythBusters: Glass is not a liquid, its an amorphous solid flow slowly, also called pseudo solid, supercooled liquid)
5. Why some objects are selectively transparent ?
6. Why some objects are selectively reflective ?
7. Why dye based filters reflect and pass through same color (different than dichroic/interference filters)?
8. How is absorption coefficient and extinction coefficient linked ?
9. Are all metals opaque ? Can a metal sheet be transparent.
Yes all of them, actually they are transparent but the extinction coefficient is so high that block even a laser pointer at few micrometer. Recently youtuber (@actionlab) demonstrated light passing through a 100 atom thick aluminum film deposited over a transparent plastic sheet.
Except this people confirmed about x-ray through aluminum foils. Again XRD is another proof but its not refraction but diffraction.
10. What is vibrational em wave ?
References:
1. Fermilab youtube https://www.youtube.com/watch?v=CUjt36SD3h8
2. On the Transmission of X-Rays through Metals https://www.nature.com/articles/091607b0
