# (Question) Monochromatic light on refraction

• Prajwal77
In summary, the color of the refracted light would remain green, regardless of the medium it passes through, as long as the frequency remains constant. This is because our eyes perceive color based on frequency, not wavelength, and the wavelength within the eye is independent of the medium surrounding it.
Prajwal77
Okay so I've got a question. If we allow a monochromatic light, say the color green to pass from air to water, what color would the refracted light be? This thought came to me because I was reading that light, when passed through an optically denser medium, would travel slower. Since the frequency of light remains constant on refraction, speed should be proportional to wavelength. So wavelength decreases as a consequence. Should the light be green or a different color?

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Prajwal77 said:
Okay so I've got a question. If we allow a monochromatic light, say the color green to pass from air to water, what color would the refracted light be? This thought came to me because I was reading that light, when passed through an optically denser medium, would travel slower. Since the frequency of light/ EM wave remains constant on refraction, speed should be proportional to wavelength. So wavelength decreases as a consequence. Should the light be green or a different color?
Are you asking if our eyes detect wavelength or frequency? Then the answer is, it doesn't matter, because the medium is the fluid in our eye, so has a definite connection between the two. But when we interpret that detection, we should interpret it as a frequency, because that is what stays the same when light passes from the outside medium into our eyes (and note that light refracts in our eyes as well, so we never actually "see the vacuum wavelength" of light).

Or are you asking how we define color, independently of how our eyes see, like if we had an instrument that reads wavelength in whatever medium it is put in, and calls that the color? If the latter, my guess is we always translate the outcome of the latter question as though it was the former question, i.e., we ask how our eyes would see that wavelength if it passed from the medium of interest, to the medium of our eyes. It's an interesting point, however, because we can in some sense count other wavelengths, like radio or X-ray, as "colors", but of course our eyes don't see those at all. In that case, I would expect that, by the "color" (including radio or X-ray as types of colors, if you will), we always refer to the instruments we actually use, which operate in air typically, or in vacuum, but not in the medium you are talking about. So that wavelength in that medium always ends up getting translated into whatever wavelength it would be in our instrument-- which means we are always talking about the frequency, not the wavelength, as the thing that stays the same in the instrument and in the observed medium in question.

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Prajwal77 said:
Okay so I've got a question. If we allow a monochromatic light, say the color green to pass from air to water, what color would the refracted light be? This thought came to me because I was reading that light, when passed through an optically denser medium, would travel slower. Since the frequency of light remains constant on refraction, speed should be proportional to wavelength. So wavelength decreases as a consequence. Should the light be green or a different color?

This is a FAQ in this forum. The point is that relevant for the colour impression is that you are seing with your eye. The sensitivity of the colour receptors in our eye are sensitive to frequency, not wavelength. But even if they were sensitive to frequency, this would not make a difference, as the wavelength of the light within the eye is independent of the medium surrounding the eye but only depends on the frequency.

Prajwal77
DrDu said:
The point is that relevant for the colour impression is that you are seing with your eye. The sensitivity of the colour receptors in our eye are sensitive to frequency, not wavelength. But even if they were sensitive to frequency, this would not make a difference, as the wavelength of the light within the eye is independent of the medium surrounding the eye but only depends on the frequency.

Thank you, that explains well.

## 1. What is monochromatic light?

Monochromatic light is a type of light that consists of a single wavelength or color. It is a pure form of light and does not contain any other wavelengths or colors.

## 2. How does monochromatic light differ from white light?

White light is a combination of all wavelengths in the visible spectrum, while monochromatic light only consists of one specific wavelength. This means that white light appears as a mixture of colors, while monochromatic light appears as a single color.

## 3. What happens to monochromatic light when it is refracted?

When monochromatic light enters a new medium at an angle, it bends or changes direction due to the change in speed of the light. This is known as refraction. The amount of bending depends on the density of the medium and the wavelength of the light.

## 4. How does refraction of monochromatic light affect its speed?

The speed of monochromatic light is affected by refraction because it changes direction when it enters a new medium. The speed of light is slower in denser materials, so the speed of monochromatic light will decrease when it enters a denser medium.

## 5. What is the relationship between the angle of incidence and the angle of refraction for monochromatic light?

The angle of incidence and the angle of refraction are related by Snell's Law, which states that the ratio of the sine of the angle of incidence to the sine of the angle of refraction is equal to the ratio of the speeds of light in the two materials. This relationship is known as the law of refraction.

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