Changing Angle of Refraction?

In summary, the angle of refraction changes when the incident angle is changed. The angle of refraction is also different for different parts of the glass block.
  • #1
FeDeX_LaTeX
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Hello;

For my physics investigation I'm investigating a relationship between wavelength and index of refraction for a medium exhibiting normal dispersion. The medium is borosilicate glass (BK7). However, I'm encountering some problems that I didn't expect.

For example, directing a red ray of light with wavelength equal to 750 nm with an incident angle of 20° gives me an angle of refraction of 18°. This was measured five times and 18° was the result each time.

However, on another day, performing the same experiment, with the same filter, the same ray box, still using an incident angle of 20°, I get an angle of refraction of 16° (2° away from my previous result). This was also measured five times to ensure that the measurement was accurate. The positioning of the protractors were identical.

Can anyone suggest why this is the case?

I assume that I accidentally had the glass block orientated the other way round (rotated 180°), which could have played a part in this difference in the angle of refraction. If this were the case, is it possible that different parts of the glass block exhibit normal and anomalous dispersion, causing this change in the angle of refraction to be observed?

Is this a correct explanation or is there an error in my reasoning/can anyone offer a better explanation?

Also: I don't understand why, for example, having an incident angle of 32° gives me an angle of refraction of 24°, yet having an incident angle of 36° gives me an angle of refraction of 22°, and an incident angle of 40° yields an angle of refraction of 27°. Is the variation of dispersion through my medium the cause for this? If my medium exhibited normal dispersion, shouldn't the angle of incidence and angle of refraction be proportional for the glass medium?

(I am using standard Oxford TEXET protractors with graded measurements of 1°, so there is an inaccuracy of +/- 0.5°, I think. But a difference of 2° is quite large.)

Thanks.
 
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  • #2
Is it also possible that these are normal results and I should not have expected an inversely proportional relationship?
 
  • #3
For an angle of incidence of 20°, the angle of refraction should be 13°. This follows from Snell's law and BK7's refractive index of 1.51 at 750 nm. Looks like something is awry with the way you are measuring angles.

I assume that I accidentally had the glass block orientated the other way round (rotated 180°), which could have played a part in this difference in the angle of refraction.
That is easily tested. Make a measurement, rotate the block, and redo the measurement.
 
  • #4
Hello;

My teacher thinks that the glass block is BK7, but he is 'not sure'. I'm unable to confirm the exact type of glass we are using. He also says that I am using the right method to measure the angles... so is there anything else that could be wrong?

I will re-do the measurements. Thanks!
 
  • #5


Hello,

Thank you for sharing your findings and questions about your investigation on the relationship between wavelength and index of refraction for borosilicate glass. It is not uncommon to encounter unexpected results and variations in experiments, and it is important to carefully analyze and understand these discrepancies in order to draw accurate conclusions.

Based on the information provided, it is possible that the change in the angle of refraction is due to the orientation of the glass block. As you mentioned, rotating the block by 180° could result in a different angle of refraction due to the different parts of the block exhibiting normal and anomalous dispersion. This could also explain the variation in the angle of refraction at different incident angles, as different parts of the block may exhibit different levels of dispersion.

However, it is also important to consider other factors that could contribute to the variations in your results. For example, the quality and consistency of the light source, the accuracy of the protractors, and the precision of your measurements could all play a role. It may be helpful to repeat the experiment multiple times and compare your results to see if there is a consistent pattern.

In regards to your question about the variation of dispersion through the medium, it is possible that this could play a role in the differences in your results. However, it is also important to note that the angle of incidence and angle of refraction are not always directly proportional, even in a medium exhibiting normal dispersion. This could be due to other factors such as the shape and thickness of the glass block.

In conclusion, it is likely that the orientation of the glass block is a contributing factor to the variations in your results. However, it is important to carefully consider other factors and continue to investigate in order to fully understand the relationship between wavelength and index of refraction for borosilicate glass. Best of luck with your investigation.
 

1. What is the angle of refraction?

The angle of refraction is the angle at which a light ray bends as it passes from one medium to another. It is measured between the incident ray and the normal line, which is a line perpendicular to the surface of the medium.

2. How does the angle of refraction change?

The angle of refraction changes when light travels from one medium to another with a different refractive index. This change is caused by the change in speed of light as it enters a new medium, which causes it to bend.

3. What factors affect the angle of refraction?

The angle of refraction is affected by the angle of incidence, the refractive indices of the two materials, and the wavelength of the light. The angle of incidence is the angle at which the light ray hits the surface, while the refractive index is a measure of how much the speed of light is reduced in the medium. The wavelength of light also affects the angle of refraction because different wavelengths have different speeds in a medium.

4. What is Snell's law and how is it related to the angle of refraction?

Snell's law is a mathematical equation that relates the angle of incidence and the angle of refraction to the refractive indices of the two materials. It states that the ratio of the sine of the angle of incidence to the sine of the angle of refraction is equal to the ratio of the refractive indices of the two materials. This law helps us determine how light will bend when passing through different materials.

5. How does changing the angle of refraction affect the path of light?

Changing the angle of refraction can cause light to change direction and bend, which can change the path of the light. This is especially noticeable when light passes through a prism, where the angle of refraction changes with each surface and causes the light to separate into different colors. It is also the principle behind lenses, which use the angle of refraction to focus or spread out light.

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