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How we see

Waves, sound and light · level 2, lesson 5 of 6

A question to start

You are reading a book by a lamp. The book does not shine. So how does the picture of the page get into your eyes?

The idea

You see something when light from it enters your eyes.

  • For a light source, like a lamp, the light goes straight from the lamp into your eyes.
  • For everything else, light from a source falls on the thing, bounces off it, and some of that bounced light enters your eyes.

So the path is: lamp → book → eye. Your eyes do not send anything out. They catch light.

lampbookeye

Worked examples

1. In the dark. Switch off the lamp and you cannot see the book, because no light is bouncing off it.

2. The Moon. Light goes Sun → Moon → your eyes.

3. A rover's camera works like an eye: it catches light that has bounced off Mars rocks.

Try it

  1. What must happen for you to see something?
  2. Draw arrows to show how you see a cat under a street light.
  3. Why can't you see in a completely dark room?
  4. Does light go out of your eyes when you look at something?
Answers
  1. Light from it must enter your eyes.
  2. Street light → cat → your eyes.
  3. There is no light to bounce off things into your eyes.
  4. No. Light comes into your eyes.

Common mistake

"Eyes send out beams to see." Eyes only catch light. The arrows always point into the eye.

Where it leads