Draw a labelled diagram of an experiment to show rectilinear propagation of light.
Let us take three rectangular pieces of cardboard A, B, and C and make holes in them at the same horizontal level. With the help of a wooden stand as shown in the diagram, we make them stand parallel to each other with holes in the same straight line. We place a source of light, for example, a candle at the other side of cardboard C and adjust the cardboard pieces such that the light is visible through the hole at A. Now, we move the cardboard B in such a way that the hole no more stays in the same straight line with A and C.
We will find that when the hole on B is moved away from the straight line, the light will not be visible from A’s end. This proves that light moves in a straight line.