I am going to measure the real and apparent distance of an optical pin placed behind glass blocks. To measure the apparent depth I will attach an optical pin to a glass block then I will place a drawing pin on top of the glass block, to determine the apparent depth I simply found the place where the drawing pin lined up with the optical pin even when I moved my head form side to side. The real depth was the distance from the optical pin to the drawing pin. This experiment was repeated using different lengths and using different sides of the glass blocks. I did each experiment twice so that my results were reliable, to do this I simply took one reading then I picked the pin up and placed it back down again to take a second reading. If the values of the readings weren’t close to being the same I then repeated the experiment until I got satisfactory results that I could use to determine the relationship with real and apparent depth.
Prediction
By looking at all the information, I predict that an object that is placed behind a material that is denser that the material from which the observer looks, then the object will look like it is closer.
Obtaining Evidence
By reading information about the topic in this coursework I have discovered what causes the effect of real and apparent distances to objects. Light travels at 3x108 m/s in a vacuum, it travels slightly slower in air and even slower through glass or water. The change of speed from when light enters a transparent material from air is called refraction. When light is travelling into a transparent material at 90o then the light will pass straight through with no direction change this is because the light travels fast in air then slower in glass and then continues to travel quickly through air again and so it looks like it hasn’t changed direction.
If a light ray approaches a glass block at an angle to the normal, its direction changes on entering and leaving the glass block. This is because the light ray slows down in glass and the image that is seen through it appears closer. The value how much closer it appears from the real distance is related to the refractive index which is a measure of how much the speed of light is changed, it is defined for each material. This is calculated by the speed of light in air divided byt the speed of light in the substance and is called refractive index.
Refractive Index = Speed of Light in Air/ Speed of Light in Material
As soon as I collected my data I recorded them in a neat table to make sure the results were recorded correctly.
I took 7 readings altogether, 7 readings are plenty of results to achieve a high level of reliability.
My table of results that I collected are as below. As I did two sets of apparent depth it shows clearly that my results are reliable.
I have drawn a very precise graph to show more clearly these results. The graph shows exactly what I predicted and therefore my experiment was successful. To get a better look in to the investigation I decided to work out refractive index as well to be able to show my results more clearly.
My results for refractive index are as follows.
Evaluation
As I did the experiment continuously until I got the readings that were reliable then I cant say that the results weren’t reliable, and so I can only come up with one possible way to make the experiment better and more reliable. As I used my eyesight to do this the one error I can come up with is human error, because I used my eyesight then this could have altered my results, to make this better I could have used a lazer beam as this would have made my results much more accurate. Also I could have used a ruler that was more precise to make my readings even better. My prediction was proved right, to sum up my experiment I would say it was successful as I managed to gather some good results that proved my prediction.
