1. Why was smoke put in the vessel to begin with? br 2. Why
By Question:
1. Why was smoke put in the vessel to begin with?
2. Why does laser look red when its wavelength in water is 475nm?
Related Question:
The speed of light reduces when it goes from rarer to denser medium. Its wavelenght reduces and frequency remains constant. What is the basic characteristics of light- wavelenght or frequency? For example, frequency of green light in vaccum is $5.45\times10^{14}$Hz and wavelenght corresponding to it is $550$nm. In water it's frequency remains the same but wavelenght reduces to $413.15$nm. Does colour is a property of medium? Moreover $413.15$nm wavelenght light and of frequency $5.45\times10^{14}$Hz correspond to blue light in vaccum.
Solution 1: The smoke scatter the light in all directions. The scattered light reaches our eyes. What we see as laser beam are actually the smoke particles that falls into the beam.
Solution 2: The color depends on the frequency of light that reaches our eyes. See below for more details.
Discussion on Related Question:
Light (EM waves) is produced by accelerating charges. Its frequency depends on the motion of these charges (e.g., their oscillation frequency). Thus, you may consider frequency as a basic characteristic of light. However, this may be an injustice to the wavelength.
As light enters a medium, ITS wavelength changes. This statement is prone to cause confusion. The light inside the medium is not the same as the light that enters it. The electric field of the incident EM waves interacts with the electrons in the medium and these electrons re-radiate light inside the medium. These two EM waves are not the same, although they are related to each other by medium properties. Thus, frequency and wavelength, both are basic properties of light. We should be conscious about WHICH LIGHT we are talking about?
Although, the mechanism of the color is more complex, let me attempt a simplified answer. We see is the objects, colored objects. The light emanating from the objects enters our eyes. The color is the property (frequency) of the light that enters our eyes. And the light that enters our eyes depends on (i) the light that emanates from the object and (ii) the transformation it undergoes while traveling in the medium from the object to the eye. Right now, I am seeing a blue-colored globe placed on the table. What I am seeing the object globe and the color (frequency) of light that is entering my eye is blue. When I am looking at the same globe through colored polythene, ITS color changes. Who is ITS? It is the light that is emanating from the globe, passing through the colored polythene, and finally entering my eyes.
But the perception of color is even more complex. A color-blind person may see the same globe as of different color (although light entering the eye is of the same color).
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