S3.9.1 For the adult
Reflection
When light hits a mirror, which way does it go?
What this chapter teaches
Light bounces off a flat mirror so that the angle it leaves at equals the angle it arrived at, both measured from the normal, a line at right angles to the mirror. A rough surface scatters light, so it makes no clear image.
Three questions to ask
There is no one right wording. Listen for the idea.
- A ray hits a mirror at 40° from the normal. At what angle does it leave?
- Why do you draw the normal before you draw the rays?
- Why can you see a wall from anywhere in the room, but see your face only in a mirror?
After the chapter, the learner can
- Show that light leaves a mirror at the same angle it arrives
- Draw rays reflecting from a flat mirror with a ruler
What they copy into their notebook
The normal is a line at right angles to the mirror. The angle of reflection equals the angle of incidence, both from the normal. A smooth surface reflects one way. A rough one scatters light.