Constructing a Hollow Glass Prism for Science Experiment

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Discussion Overview

The discussion revolves around the construction and measurement techniques of a hollow glass prism used for determining the refractive indices of fluids. Participants explore the implications of glass thickness on measurement accuracy and the application of Snell's law in this context.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant describes constructing a hollow prism and measuring the refractive index of water, questioning how to account for measurement error due to glass thickness.
  • Another participant suggests that measurement uncertainty for angles is influenced by the glass's thickness and questions the validity of measuring at an incidence angle of 90 degrees.
  • A participant acknowledges a misunderstanding regarding error measurement in the hollow prism, noting that the error will vary depending on the fluid used.
  • One participant proposes applying Snell's law to calculate expected angle changes when light passes through the glass sides, emphasizing the need to consider different angles of incidence.
  • Another participant points out that if the glass faces are parallel, the angle of refraction for the first face should equal the angle of incidence for the second face, questioning the rationale behind potential errors.
  • A later reply indicates a realization that there may be no error in measurements, as the angles of incidence and emergence remain consistent across the prism's faces.
  • One participant notes the potential for imperfections in the method but suggests that it could yield a reasonable estimate for refractive indices.

Areas of Agreement / Disagreement

Participants express varying views on the impact of glass thickness on measurement accuracy and the nature of errors in the prism setup. There is no consensus on the best approach to account for these errors, and the discussion remains unresolved regarding the implications of different angles of incidence.

Contextual Notes

Participants mention potential sources of error and imperfections in the experimental setup, but specific limitations or assumptions are not fully detailed.

Who May Find This Useful

This discussion may be useful for students and educators involved in experimental physics, particularly those interested in optics and refractive index measurements.

croslali arno
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i have recently made a hollow prism for my science exhibition in my school ... to find refractive indices of fluids.

i made it using 3 rectangular pieces of glass (0.5cm) on a glass triangular base ..with obviously a hollow part in the middle
it worked perfectly fine with water i got n=1.33
then my sir came ahead and asked me a question ... how do you find the error in the angle of refraction due to using the thick glass ... i didnt know ..
this is where i reached .. glass is amorphous
so i measured the angle of incidence to be 90 degrees and then i measured the angle of refraction(without anything in the middle of the prism)
i found the difference (which is 1 degree) and multiplied by 2 (as i just found error of 1 glass.)
is my theory correct?
 
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This looks like the measurement uncertainty for angles. The glass will influence the measurement if it does not have the same thickness everywhere, but with an angle of incidence of 90 degrees I don't see how you want to see that.

What did you get as refractive index for air?
 
i think i got my answer my theory was just wrong ...
the
 
@mfb
mfb said:
This looks like the measurement uncertainty for angles. The glass will influence the measurement if it does not have the same thickness everywhere, but with an angle of incidence of 90 degrees I don't see how you want to see that.

What did you get as refractive index for air?
i know where i went wrong ... actually you can't find the error of the hollow prism .. it is just like you have a very small glass prism in a water/liquid prism .. the error in the measurement of r will be different for each case
 
IF the glass sides have flat, parallel sides, how much would you expect the angle to be changed by passing through them, with air on both sides? Apply Snell's law at each surface. It would be very easy to calculate the result for a small angle between the faces - Snell's law again. What error can you permit in your overall measurements?
 
it would differ for different angle of incidences ... because it is a sine proportion ...
 
croslali arno said:
it would differ for different angle of incidences ... because it is a sine proportion ...
Why, if the faces are parallel? Angle r for the first face is the same as angle i for the second face.
Why would this not apply?
 
okay guys ... i figured it out
i think there will be no error ..
thank you sophiecentaur
it is because the angle of incidence will be the same as angle of refraction on face 1 as well as face 2 .
there will be lateral deviation but we don't actually need that ...
our aim is the angle of incidence and the angle of emergence and we get that ...
this is the pic of my prism if you want to see it
DSC00815.JPG
 
You should find this an interesting exercise. Of course, the method is full of possible imperfections and sources of error but you should get a good ball park figure for water and some other liquids. It could be interesting to see how the result changes when the path through the prism is symmetrical and when it's not. How do you plan to plot the ray paths?
 
  • #10
we have a soft wood board and pins .. the classic good ol' lab ways.
thanks how do i close this thread?
 
  • #11
Just stop writing - it will slowly sink to the bottom!:)
Good old board and pins. I don't think the glass thickness will affect your accuracy too much.
 

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