Light, Sound and Waves

The river crossing

Teaching Guidance for 11-14 Supporting Physics Teaching

A teaching anecdote

We're sure you'll find a story like this one to share with your class.

I was out walking with a friend when we came to a stream which was pretty wide (about 10 metre). It had been raining quite a bit in the previous few days and the stream looked full. I wasn't too sure about whether we could cross here. Perhaps we should look for an easier place farther down-stream. My friend would have nothing of it. It doesn't look too deep to me. I'm going to take my boots off, roll my trousers up and wade across. And so he did. In the very first step he lowered himself into the water from the bank, slipped and found himself almost waist deep in the stream.

I could feel an explanation about refraction, plus real and apparent depths coming on, but couldn't manage it through my laughter.

Teacher Tip: Work up a good story of your own about real and apparent depth, with illustrations.

is formalised by Law of Reflection
can be exhibited by Progressive Wave
has the special case Total Internal Reflection
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