## PHYS110-How Things Work

### Notes on Refraction of Light

You should have observed the following when viewing the two objects on the chalkboard.

Figure 1. Light refraction through a plastic rectangular shape

Figure 2. Light refraction through a triangular shape.
Rectangle
Figure 1 shows light passing through the rectangular piece of plastic. It refracts when entering and leaving the plastic. The dotted lines are the lines normal to the interface between air and plastic. As the light enters from the left it bends toward the normal line because it is going from a lower index of refraction to a higher index of refraction (it is slowing down upon entering the plastic. As it leaves the plastic it bends away from the normal line because it is going from a higher index of refraction to a lower index of refraction (it is speeding upon leaving the plastic).

Prism
Figure 2 shows light passing through the triangular piece of plastic. It refracts when entering and leaving the plastic. The dotted lines are the lines normal to the interface between air and plastic. As the light enters from the left it bends toward the normal line because it is going from a lower index of refraction to a higher index of refraction (it is slowing down upon entering the plastic. As it leaves the plastic it bends away from the normal line because it is going from a higher index of refraction to a lower index of refraction (it is speeding upon leaving the plastic).

In the rectangular case, since the two interfaces are parallel, the light emerges from the rectangle at the same angle it enters. For the triangle, this is not the case. Because the two surfaces are not parallel the rays end up coming out at a different angle than they entered.

Dispersion Dispersion results because different wavelengths (or colors) of light travel at different speeds. Another way to say this is that different wavelengths have slightly different indices of refraction. Thus for the triangle shape the rays refract differently and since they do not emerge parallel to in incident ray, different wavelengths emerge at different angles. Shorter wavelengths refract more than longer wavelengths, so this means that the order of colors will have longer wavelengths (like red) on the top and shorter wavelengths (like blue) on the bottom.

Refraction Through Semi-circular Dish
Your data should show that as the angle of incidence increase the angle of refraction also increase, but not as much. This means that if you plot one angle against the other it will not follow a straight line at 450. This is the reason to draw the reference line on the graph along with your data - to compare and see that there is refraction taking place.