Why Doesn't a Drinking Straw Refracted in a Glass of Water Change Color?

The straw is not a prism. Straws are opaque and do not pass/filter light.

Interesting question!

Because in a prism, the sides are flat and able to linearly amplify the visible spectrum range to be able to delineate smaller changes in wavelength. In a glass however, the side is curved. Therefore, it cannot perform the amplification and show the colors. Since this is a two-component (water and glass) medium, there is the refractive distortion. This is the way I understand it but, as I am no optics expert, I may be talking out my a$$.

Because in a glass there is not enough water to filter the any of the colors to make a visable difference to the eye.

Ordinarily room light is entering the glass from all directions, so the wavelengths are scattered and mixed. A rainbow occurs when a strong beam of light from one principle direction is refracted.

Try putting the glass of water and straw in a dark room and shining light onto it from an old slide projector or other bright collimated (broad spectrum) light source. Perhaps then you may see a faint rainbow effect around the edges of the straw. Remember that the straw will be filled with water, so at the water/straw/water interfaces there is not a lot of refraction occurring; the refraction occurs at the top surface of the water at the water/air interface.

If the straw is already colored, say red, there's nothing else to spread out, so it remains red.

If the straw were emitting white light, then that light would spread a small amount (like an off-kilter 3 color comic book) and you'd see a very very tiny dispersion. Put the straw behind the glass and you'll get more. But, it's very tiny, very hard to see.

Remember, cheap camera lenses cause the same effect and, for low magnification or short lenses, are not corrected.

Of course, the other problem is that you usually see the straw near the center of the glass where the effect is less. Turn the straw sideways so that one end is near the side of the glass and you might see more.

speed of light= wavelength x frequency

Well if the speed of light is reduced then what changes? frequency? or wavelength? or both?

Which still leaves the question in my mind, why does the color not shift? since the distortion in the pencil is a function of a change of the equation?

Wavelength changes. Frequency is a characteristic of the energy of the light source and can't change.

In that case shouldn't there be a color shift ala Doppler?

Is it moving? Are you moving?

If wavelength changes it's like what happens in a doppler event.

You're letting the tail wag the dog.

Sunlight is almost like a laser beam, highly collimated. Usually one is far away from the mist causing the rainbow. The two facts ensure that there is adequate angular separation between the different colours for us to see the rainbow. The same thing does happen whenever there is a refraction, even in a glass of water. As usbport said, the light beam in a room is scattered light with negligible collimation and one is quite near. Whatever dispersion takes place leads to a jumbled wave front of scattered light of different colours, which we perceive as white light. However, whenever you see light from a point source like a tungsten bulb through a cut glass artifact or a diamond jewel you can see the colours. Every evening I see a rainbow whenever I water the lawn with a spray head and the slanting sun rays come from behind. Bioramani

Frequency and wave length are just reciprocals, so both change.

That is only true while the velocity is constant. Since the velocity changes when the medium changes, that statement is no longer valid in this situation.

I am pretty sure that the frequency of ANY waveform is the reciprocal of the wavelength (which is also called the period of oscillation). They are Fourier transforms of one another. The velocity has nothing to do with that.

The period is the reciprocal of the frequency. T=1/F (Seconds/wave)=1/(waves per second). The wavelength is a distance, not a time, so it can NOT be the reciprocal of frequency. λ=V/F. (meters)=(meters/second)/(1/second).

No higher math (beyond high school algebra) is needed, but velocity is!

Oops. I stand corrected. Thanks.

Whoa...! Just read the wiki article, it's gonna take a little mental percolating to wrap my mind around Goethe's thinking!

Interestingly Goethe's not postulating a theory on the fundamental process underlying the perceived phenomena is reminiscent of Newton's answer when asked to explain how gravity works the way it does he answered, "I feign no hypothesis." -- but he was able to quantify gravity's action into a predictable mathematical model.

That deserves MUCH more than just a GA, but that's all I can give you for now...

To the OP: I suspect that the color DOES change, Just not enough for it to be obvious. I'll have to think some more about this...

The separation of colors you refer to is called dispersion. It does occur with all white light, but the straw is so large that the color separation can only be seen at the edges of the straw. If you wish to see the dispersion clearly, you should do what you do with a glass prism to see the colors. Create a dark room and allow a narrow ray of sunlight to shine through the water. The colors will be visible on a sheet of white material.

Luther M

You are observing the reflection phenomena and noy the refraction.

refraction produces the bending of the light beam in the water but the straw image is a reflection phenomena. you are seeing the image of the straw. There will be, probably, several images of the straw, each with a different colour, reflected, but you would need to magnify the image a lot to experience the refraction of the light arround the straw.

NO! The image of the portion of the straw below the water is refracted, not reflected. The portion of the straw above the water is directly visible, neither reflected nor refracted.

Please read carefully before the (NO!).

There is a refraction. The refraction index of the water is different from the Air (which has to do with the different speeds) and the difference between the different frequencies of white light will not be enough to see at the distance being observed. So you only see image of the straw and not the refracted light as in a rainbow... you need more distance (or a magnifier...) Or what the hell waisting time on such a simple thing...

No one so far has it, and simple: Neither the glass nor water exhibits properties as a prism. Enough said.

Optional: google prism

Not nearly nuff said. A glass does indeed cause dispersion. The speed of the various colors is different and that shows up at the edge as though you had a mis-aligned 3 color press.

The straw is an object viewed or seen with the help of the refracted light.

Dickson.

If you had a very slender white straw and a black background, you should see a blue and red border because of the different refractive index of red and blue light. It may be rather subtle.

Light from all directions fall on to the surface of the straw gets reflected and then refracted at the water air interface. Since the light falling on to the straw is not original source but only a reflection from the surroundings and therefore can be considered as small beam of white light from all directions -millions of them reflecting back from the straw surface. If you consider each beam is dispersed in to a spectrum , there will be millions of spectrum each superimpose on the other and the net effect will be only a white light and and not a spectrum. As for the light falling on the edges, there are no material adjacent to it ,resulting in a thin multicolor spectrum.