# Refraction problem (temperature dependence)

• B
Hi Everybody
I am doing an experiment for a school project where I have chosen to see is the index of refraction changes in a body of water when the temperture changes. So I am using the angle of incidence and refraction to measure using snells law.
The Problem:
Obviously I need a container to hold the water but it will effect my results and how can I resolve this.
Thanks for the help

Last edited:

sophiecentaur
Gold Member
2020 Award
but it will effect my results
If the light enters the water at the top surface (air / water) the container will have no effect. Not as convenient as doing it with a glass block on a bench but, if you can get hold of a container with flat sides, you could put the block against a screen with graph paper on it. Problem is that the RI doesn't change much over a convenient range of temperatures. (Look this up and make sure).
Did you consider using the 'pin' method, rather than just shining a ray? Higher accuracy.

[QUOTE=" 'pin' method, rather than just shining a ray? Higher accuracy.[/QUOTE]
Hi
what is the pin method?
Is this

Last edited:
ZapperZ
Staff Emeritus
I

Its the same one :).
The post which you mention my teacher told was really difficult and somethings didn't apply for the requirements. so this is the new one.

That one was really difficult and this one isn’t? I think it is the other way around! You are trying to find a variation that is rather small which can easily be beyond what you might be able to detect without expensive, accurate equipment.

Zz.

nasu
That one was really difficult and this one isn’t? I think it is the other way around! You are trying to find a variation that is rather small which can easily be beyond what you might be able to detect without expensive, accurate equipment.

Zz.
My teacher told me that it wasn't really an experiment and that I was proving a the theroy and that I needed first hand evidence but he said this one was better.

ZapperZ
Staff Emeritus
My teacher told me that it wasn't really an experiment and that I was proving a the theroy and that I needed first hand evidence but he said this one was better.

What do you, and your teacher, think is “first hand evidence” to verify a theory in physics?

Zz.

sophiecentaur
Gold Member
2020 Award
My teacher told me that it wasn't really an experiment and that I was proving a the theroy and that I needed first hand evidence but he said this one was better.
Hmm. I think your teacher may just be being 'controversial' about this. Look up some facts about the RI of water variations with temperature and ask him if he seriously thinks a simple experiment will show the variation over a convenient and safe range of temperatures that can be measured accurately and has he a method to ensure that the water temperature is uniform.
How many hours of uninterrupted experimental time (and lab space) will he make available to you?

Pin method: I was at school long before laser pointers were available and this was far better than the incredibly naff light boxes that were available but I still think the pin method is preferable for a bench top experiment. Your YouTube video is one example and it actually does the job much better than a laser pointer could. Google Images "Optical pin methods' for many other examples. They are mostly done by sticking (vertical!!) pins into a horizontal board with paper on it and using your eye to line them up so that all the pins are hidden by (behind) the one nearest you. The pins are a great, semi permanent record of the experiment and you can draw ray lines and trace the outline of your mirrors / glass blocks etc. and measure angles very accurately after the equipment has been put away.

sophiecentaur
Gold Member
2020 Award
@Elbraido
This isn't really on the School syllabus, I think, but we did a really clever optics practical in Uni (1966) which was based on the Abbe Refractometer. It is based on the Critical Angle (below which Total Internal Reflection stops) and a small amount of fluid, sitting the back of a glass D is all you need (and you can use the pin method to see the angle where the ray stops escaping from a surface. Look it up. It is potentially quite simple and the temperature of the block / water drop would be easy to measure and maintain.
This refractometer is good for analysing tiny samples of liquids and can tell you the concentrations of solutions etc.

@sophiecentaur
Thanks for your help. Firstly this a do at home experiment with our 3 week holiday coming up and I am also in Australia which I beleive is differernt to the syllabus in the UK. Plus your second comment about the Critical Angle, I really like it and i might consider it but could you please send like a diagram of how you would be seting it up. I will add a the assignment notifaction for clarification.
THANKS for the great help so far

#### Attachments

72.6 KB · Views: 191
sophiecentaur