Activity 1.6 - Exploring plane mirrors

• Understanding that light rays travel in straight lines
• Understanding that plane mirrors reflect light
• Understanding that the angle of incidence equals the angle of reflection

The activity begins with students being posed a question of the form: ‘If you look through a straw at an object, what direction must the light travel from the object to your eye in order for you to see it?’

The students are then asked to consider the same question but for two straws forming a V-shape. What might one use to get light to alter its direction so that light passing into the first straw could be seen through the second straw? The teacher should guide the discussion towards the notion of ‘reflection’ from a mirror.

The students can then use Worksheet 1.6 and clamp a mirror at one edge so it is held vertically by a retort stand. The bottom edge of the mirror should be in contact with the mark on the paper. They can then position a drinking straw at some random angle in front of the mirror and attempt to position a second straw so that when they look through it, they will see the reflected light that passed through the first straw.

The students should then be asked how they would need to alter the setup if they changed the angle of one of the straws, or the angle of the mirror.

• Do you notice anything about the angles the straws have to be in order for light to pass from one to the other?
• Does this relationship hold when the mirror is angled?
• What would happen to light at different points on the mirror if the surface of the mirror was curved inwards or outwards?