Prediction
I predict that whatever the angle of incidence is, it will be larger then the angle of refraction because the light will be entering something denser, so the wave nearest the “normal” will enter the block first, causing the ray to turn towards the normal, reducing the angle size.
Keeping the experiment fair
In this experiment I will be only changing one variable, which will be the size of the angle of incidence. This means I will have to have to keep all the other variable the same. To do this I will use the same ray box, with the same current and voltage passing through it, the slit the same size and the same distance from the bulb. The same ray box and the same protractor to measure the results. A Sharp pencil and the use of a ruler to draw the rays of light will help keep the result accurate.
Equipment
Method
Shinning a ray at light into the ray box at 90º to record the normal. Then the ray of light will be shone into the glass block at the same point of entry except that the angle of incidence will be changed to 80º (using a protractor to measure the angle). The line of incidence and exit will be recorded and then the line of refraction drawn in, linking the 2 of them up. I will then use the protractor to record the angle of refraction. I will then repeat the experiment with the angle of incidence changing to 70º, 60º, 50º, 40º, 30º, 20º and 10º. If there is enough time I will repeat the experiment again to get a second check of the results.
Preliminary Work
Before I actually do the experiment, I thought some preliminary experiments might be useful. For a start the most accurate results will need the thinnest rays of light coming from the ray box. I changed the distance from the bulb to see how that affected the width of the ray of light. The table below show the results of that experiment.
These results show that the further away from the further away from the bulb you get, the thinner the ray of light. This is because the further away from the source of light you get, the smaller the amount of rays that can be given off at an angle and thus widening the ray, decrease. It is obvious that using a thinner slit in the slides will help to thin the ray. So because of this, I’m using the narrowest slit in a slide I can find.
Results
I did the experiment and these are the results I got. The graph is attached.
The reason that there are two Refraction results is because I repeated the experiment. The last column is the average of the two sets of results.
Analysis
My results show that as the angle of incidence increases so does the angle of refraction. The angle of Incidence was larger then the angle of refraction. This is because the light will be entering something denser, so the wave nearest the “normal” will enter the block first, causing the ray to turn towards the normal, reducing the angle size. Once the angle of incidence got past 60º, the angle of refraction increased less. I think this is because the further away from the normal the angle of incidence got, more of the wave hit the glass block first. As more of the wave hit the glass block, a greater percentage of the light slowed down as it hit the glass. This meant that the light bent slightly more then before. There does not however seem to be a numerical pattern shown on the graph but this could be because of the way the result were recorded (see evaluation). Another useful thing to mention is that as speed slows down as it hits the glass block, so the wavelength and frequency would decrease also. This because of the formula for speed which is frequency x wavelength. So in order for the speed to decrease, the frequency and wavelength will have to decrease as well.
Evaluation
My data does seem to be reasonably accurate as all but one of the points join up in to a line of best fit. The point on the graph at 50º, for the angle of incidence, did not fit into the trend though. This could be for a number of reasons. It could be that one or both of the results taken to record the average was inaccurate. This could be because the angle of incidence was set correctly, the result was read incorrectly as the results were taken by eye or the way the experiment was done was inaccurate, all the other results could have been inaccurate and this could be the only accurate one, but that is unlikely. Our method though was pretty inaccurate. It all counted on eye judgement which isn’t very accurate. So because of this I think the reason for the odd result was an incorrect reading from me or one of the people helping me with the experiment, as the evidence (the inaccuracy of the result taking) points towards this conclusion, but we shall never know for sure. We could look at other results in the class to see if their results matched ours, as the odd result could be there on all of them, but it would still just make us certain about our idea, when it could be something different. The experiment could have been done using far more precise measuring equipment then a protractor. The result could also have been measure and recorded by a computer, which (if set up correctly) would be far more accurate, but we just didn’t have the resources, time or money to do that. One thing we could have done to make the experiment more accurate though is to take more results and take the average. This would have made the results more accurate.
