Tracing the Path of Light through a Prism
Let us now trace the path of light through a prism.
Place a prism on a white sheet of paper with the triangular face on the sheet and trace its boundary ABC.
Fix two pins T and S on one side.
Place the prism on the boundary ABC.
Looking through the other side fix two more pins Q and R in such a way that the all four pins appear to be in the same line.
Remove the pins and mark their positions.
Join TS and RQ and extend them to meet the faces of the prism at P and O respectively. Join PO.
TP represents the incident ray
PO represents the refracted ray
And OR represents the emergent ray which is bent towards the base.
Let PN and ON be the normal at the points P and O respectively.
And let i be the angle of incidence and r the angle of refraction.
If the incident ray TP is extended forward and the emergent ray RO backwards, they meet at M, forming the angle OML.
Measure the angle OML.
This angle is called the angle of deviation.
Angle of deviation is the angle through which an incident ray deviates.
Repeat this for different values of angle of incidence.