Colour change due to refraction

[zorro]

Homework Statement

A source of yellow light in air is observed by a diver inside water. If the wavelength of yellow light in air is 6000A, then find its wavelength and colour as observed by the person.

I found out the wavelength inside the water as 4500A.
The colour must change as the wavelength changes. It might be blue.
However the answer says 'yellow colour'

 

[gneill]

The diver only ever "sees" light that is passing through the aqueous humour of the eye.

 

[zorro]

Yes and that is a light with wavelength 4500 A which is not for yellow colour.

 

[gneill]

Yes and that is a light with wavelength 4500 A which is not for yellow colour.

No. Draw a diagram showing the complete light path from the source to the retina. Label the wavelength in each of he media it traverses.

 

[zorro]

Colour of a light depends on its wavelength. Do you agree with this?

 

[gneill]

Colour of a light depends on its wavelength. Do you agree with this?

Yes. What is the wavelength of the light when it reaches the retina? Not when it reaches the front of the cornea of the eye, but the retina in the back.

 

[zorro]

So do you mean that there is a refraction taking place at the eye lens which possibly changes its wavelength back to the original?

 

[Dadface]

Yes but there is also refraction due to the cornea and the humours.On reaching the retina the light has to pass through the cornea,aqueous humour,lens and vitreous humour.

 

[gneill]

So do you mean that there is a refraction taking place at the eye lens which possibly changes its wavelength back to the original?

What do you think? The aqueous humour is just another medium for the light to pass through.

What we call yellow light at 6000A (in vacuum or (approximately) air), is not 6000A when it hits our retinas. But we still call it yellow light because that's what we measure for vacuum or air wavelength for light that we choose to call "yellow".

 

[zorro]

But the question does not give any values of refractive indices of these things. How can we deduce that it is yellow?

 

[gneill]

But the question does not give any values of refractive indices of these things. How can we deduce that it is yellow?

Has the medium in the eye changed in any way for the two cases (in air and under water)? The wavelength perceived by the retina is always the wavelength of the light as it will be inside the eye.

 

[Dadface]

And following on from gneills comment above the frequency perceived is always the frequency of the light as it will be inside the eye.I prefer to think of colour perception in terms of frequency rather than wavelength one advantage being that there is no change of frequency during refraction.

 

[zorro]

Thank you!

 

[ehild]

Seeing starts with absorbing a photon by a molecule in the cones and rods in the eye. The excited molecule undergoes through a structural change, and this ignites a process resulting an electric impulse sent to the brain.
A molecule can absorb a photon if the photon energy matches the difference between two energy levels.
So it is the energy of the photon which counts. Colours are assigned to wavelengths in vacuum, as earliest spectrometers measured absorption or emission of light in terms of wavelength.

See http://en.wikipedia.org/wiki/Visual_phototransduction

ehild