Refractive index simulation (Algodoo)
This is a way that you can do this experiment without using a protractor. Consider a ray of light passing through the two semicircles shown. The left hand circle has the same refractive index as air (1.0) and the right has refractive index the same as glass (1.5). The ray of light is arranged so that it passes though the centre of the circle. This is all a bit contrived but you can make it easily with the simulation programme Algodoo.
According to Snell's law
So the refractive index
Setting up Algodoo
Following the instructions in the screencast set up 5 lasers passing through the centre of the circle at a range of angles. When finished take a screenshot of the simulation, copy it to paint crop it to the size you want and add a central line to the image. Save the image on your desktop ready for analysis.
Analysing the image
You can analyse the image in paint by simply taking the line tool and drawing a vertical line between two points as shown below. The length of the line is displayed in pixels at the bottom of the page. Alternatively you could use loggerpro image analysis.
Measure the different values of y1 and y2 and enter them in a table.
Plot a graph of y1 vs y2, the gradient of the best fit line should represent the refractive index of the right hand block.
You could also do this with a real semicircular glass block and a ray lamp. The left hand air circle is simply drawn on paper.