Fig. 10.1 shows a notice written in white chalk on a black board. On a dark evening Pena uses a torch to look at the notice. (a) On Fig. 10.1, draw a ray of light to show how Pena sees the writing. (b) Explain why the writing stands out against the dark background.

Draw a ray of light originating from the torch, travelling towards and striking the white chalk writing on the blackboard.

From the point where the light ray hits the writing, draw a second ray of light reflecting off the writing and travelling directly towards Pena's eye. This shows the path of light that allows Pena to see the writing.

The white chalk writing reflects a significant amount of the torch's light, while the dark blackboard absorbs most of the light and reflects very little.

This difference in reflection causes the white chalk to appear much brighter than the dark background, making the writing stand out clearly to Pena's eye.