Take a small piece of long rubber pipe and place a candle on a table. Light the candle. Stand a little far away from the table and see the candle flame through the pipe. It is visible. Now bend the pipe or move it to the right or left and again look for the candle flame. The candle flame will disappear. This shows that light travels in a straight line.
The reason is that light rays coming towards our eye through pipe is stopped due to bend. Since pipe is made up of opaque material, so light cannot pass through it. Hence light cannot reach our eye, due to which candle is not visible to us. This shows that light travels along a straight line.
