Refractive Indexes of Different Colors of Jell-O

[Imagina7ion]

Homework Statement

Why is the index of refraction in lighter colors of Jell-O higher than the index of refraction of darker colors of Jell-O, and why is the speed of light faster in lighter colors of Jell-O?

Homework Equations

The Attempt at a Solution

I know the refractive index of the different colors of Jell-O are between 1.30-1.40.

Note: I'm an 8th grader, I just need help with my Science fair project.

 

[Delphi51]

Welcome to PF, Imagina7ion!
Your question is unusual; we usually just measure or look up the refractive index and use it rather than asking why. I am very surprised the color of Jello affects its refractive index.

You should read the Wikipedia article, which has some information on how the interaction of light with atoms determines the speed of light in a material: http://en.wikipedia.org/wiki/Index_of_refraction
Note from the article that the index of refraction is c/v where c is the speed of light in a vacuum and v the speed of light in the material. The index is the "slow down factor" for light in a material. Since v = c/n the speed of light in the jello with the highest index will be slowest.

For your project, you must be extremely careful measuring the index to be sure the effect you found is convincing to the judges. You might let us know how you are measuring the index so we can offer suggestions - it must be awkward to see a beam of light inside the Jello and mark its location. Also difficult to get a flat surface of Jello with an easily measurable direction. Certainly you will need to repeat the measurement at least a dozen times and take an average, perhaps eliminating the highest and lowest measured values.

Enjoy your project!

 

[Imagina7ion]

For my project, I measured the refractive index by:

1. Positioning Jell-O at an angle(s) (41, 50, 60 degrees)
2. Shine a laser straight through
3. Find the angle of refraction (usually around 12-14 degrees)
4. Substract angle of refraction from angle Jell-O is positioned at (this will be the second angle)
5. Find the SIN of Angle 1 and divide by the SIN of Angle 2

To find the speed of light I divided the speed of light by the refractive index of whatever color Jell-O was measured.

Let me rephrase my question:

How do different colors of Jell-O affect the speed of light inside the medium? Why is it faster in lighter colors than in darker colors. I am trying to answer this question so I can put it in my conclusion for the poster/final report.

 

[Delphi51]

I don't quite understand your setup for measuring the angles. Could you sketch a diagram? The usual way to do it is with a semi-circular "piece" of the material. That way the beam emerges from the material at an angle of zero and does not bend - so you can measure the angle of refraction A2 outside the material.

There is a way you could make semi-circular pieces of Jello. Visit the school lab and ask for a circular Petrie dish that is divided in half. Fill half of it with Jello and let it set. Then you just ignore the empty half; the light will not bend noticeably as it goes through the thin plastic on the unused half.

Thinking further about this, I suspect the index of refraction varies with different batches of Jello. More water would very likely reduce the index. More powder would increase it, perhaps even the portions of sugar and gelatin would vary from one box to another. To make a convincing argument that the index varies with color, you would have to mix up Jello batches from a few different boxes, very carefully measuring the weight of the powder and water used. Your school lab should have accurate mass balances you could use.

Another approach would be to use clear gelatin and food colouring, making all the colors from the same batch. This would deal with the possibility that the Jello company puts more sugar in with one color than another. You could also write to Jello and ask about that.

 

[rwisz]

I would like to first clarify that the refractive index of a material is not dependent on its color. It is a property that is determined by the material's density and the speed of light in that material. However, in the case of Jell-O, the color may affect the speed of light due to the presence of different pigments or dyes that may absorb or scatter light differently.

The reason for the higher refractive index in lighter colors of Jell-O could be due to the presence of more water molecules. Jell-O is mainly composed of water and the lighter colors may have a higher water content compared to darker colors. This higher water content may lead to a higher refractive index, as water has a higher index of refraction than the other components of Jell-O.

As for the speed of light, it is affected by the density of the material. Light travels slower in denser materials, and the presence of more water molecules in lighter colors of Jell-O may result in a lower density and therefore a faster speed of light.

However, it is important to note that the difference in refractive index and speed of light between different colors of Jell-O may be very small and may not have a significant impact on the overall properties of the material. Other factors such as the concentration of gelatin, sugar, and other ingredients may also play a role in the refractive index and speed of light in Jell-O.

I hope this helps with your science fair project. Keep up the curiosity and keep asking questions!