Assignment Flashcards
Title
Law of refraction
Aim
To investigate how changing the angle of incidence effects the angle of refraction
Underlying physics
Snells law states that the ratio of the angle of incidence to the angle of refraction of a wave as they change is constant. This means that as the angle of incidence increasing the angle of refraction increases accordingly. This constant is represented by the n and its know as the refractive index. The refractive index of of material is a measure of the change in the speed as it passes from a vacuum into other material. Since it’d a constant the refractive index for each material will have own value for exmaple air is 1 and water is 1.33. This xan all be shown by the formula
N =
With sin1 being the angle from the normal in air and sin 2 being the angle from the normal in the median.
There are 3 factors that our effected by the xhange in median. These are angle speed and wavelength. As the light goes from air into a different material the speed of light decreases and so does the wavelengths this means that since they are both smaller the angle will be too. Once it leaves the material and goes back into air it increases again. This xqn be shown in a diagram.
[Digarm]
As you xan see as the light entered the angle of reflection drescreaeed once it left again it increased. This is because the refetive index for glass is greater than air
One thing that isn’t effected by the change is frequency. This means that jts that it stays the same throughout all material. The refractive index is also determined by the frequency. So if the frequency is increased the refractive also increased.
For my experiment we measured sin I and sin r and plotted the graph that should look like this.
Since n=
And n is constant then we can use thr gradient yo give us the refctiavtuve index.
Evaluation points
- dark room
-reapt
-line stead
Method
Using a protractor and a ray box
We change the angle of incidence and then measured the corresponding angle of refraction
Analysis
Since n is a constant then the refractive index will be the gradient of my graph
Work out gradient
Since the refractive index for perspex glass is 1.5 and i got 1.4 it proves that my raw data values were accurate ans consistent.
This xan be seen as my because as my angle of incidence increased from 10° to 80° my mean angle if refection also increased from 7.1° to 46°. This is then proven by my graph since jts a straight line that is very close to the origin. This shows that the sin I and sin r are proportional to eachother. This trend is then backed up for a final time by my second source. They plotted the same graph as we with sin r vs sin I and also got a straight line. This then backs up my relationship that sin r and sin i are proportional ti eachother allowing for n to be a constant.
conclusion
In conclusion as you increase the angle of incidence the angle if refraction also increases. This js shown by my graph raw data and second source
Dark room
One thing that made my experiment good is that I did my experiment in a dark room. This was good for my experiment because it meant that when I marked my lines for the angle of refraction I could clearly follow the line and mark it down correctly and precisely. This can be seen throughout all my data reapts because they were all the same or close in value. This shows that my results were reldilbe and consistent
Wide lines
Another thing that was difficult un my experiment is that as the angle of incidence increased the width of the line of refraction increased. This makes jt more difficult to get an accurate angle because you have to estimate the line jn the middle. This effect can be seen through my uncertainties. For my smaller angles my uncertainty ranges from 0.2 to 0.4 whixh was low. For my larger angles my uncertainties ranged from 0.6 to 0.8 which is quite high. This is because we had to estimate, making it less accurate. To minise this effect we could have used a led to focus jt more and make it easier to read. If we had done this then we would have had more accurate results.
Repeat
One thing that would improve my experiment if I would reapt 2 more times. I would so that I would improve my uncertainties for the larger angles since they there js the 0.6-0.8 range which is alot higher than my smaller values. If I had done this then I would have gotten more results allowing my avager to be more accurate ans representing of the actual angle of refraction.
