1) Do this experiment in the dark room.
2) Take a prism and place it on a table near a vertical white wall.
3) Take a thin wooden plank.
4) Make a small hole in it and fix it vertically on the table.
5) Place the prism between the wooden plank and wall.
6) Place a white light source behind the wooden plank.
7) Switch on the light.
8) The rays coming out of the hole of plank become a narrow beam of light.
9) Adjust the height of the prism such that the light falls on one of the lateral surfaces.
10) Observe the changes in emerged rays of the prism.
11) Adjust the prism by slightly rotating it till you get an image on the wall.