Question

How can you explain the straight-line motion of light?

Answer 1

1. Observe the objects, the formation of shadows and the path of light as shown, in the figure. 

2. Similarly draw the shadows for the objects given in the fig. Extend the path of light and draw a shadow on the given screen.

3. We have drawn arrows in the above figures assuming that light travels like rays that are straight. 

4. We can predict the shapes of the shadows only when we consider that light travel as rays along a straight path. 

5. In ancient days, by observing the shapes of shadows people came to an understanding that light travels in a straight line.

Answer 2

Light travels in straight lines primarily due to the fact that light is a wave. However, light can change its path (away from a straight line) when it is incident on certain obstacles. This effect is commonly reffered to as diffraction. Since diffraction is very small effect, light is generally assumed to travel in straight line .