S3.9.2 For the adult
Refraction
Why does a straight stick look bent in water?
What this chapter teaches
Light slows down going from air into water, and bends towards the normal. Coming out, it speeds up and bends away. The eye traces light back in a straight line, so a stick looks bent and water looks about three quarters as deep as it is.
Three questions to ask
There is no one right wording. Listen for the idea.
- Which way does a ray bend when it goes from air into water?
- Why does a stick look bent at the surface of water?
- Why can you see a coin in a cup when it is full of water, but not when it is empty?
After the chapter, the learner can
- Explain why a stick looks bent in water
- Show how pouring water into a cup makes a hidden coin appear
What they copy into their notebook
Light slows down in water. A ray going in bends towards the normal. A ray coming out bends away. Eyes trace light straight back, so water looks shallower and a stick looks bent.