The Fairy-Land of Science · Lecture II, part 2 · Part 2: Lecture II: Sunbeams and the work they do
5. Sunbeams are waves, and a rainbow on the wall
Goal: Your child can say that light travels as tiny waves and that white sunlight is a mixture of all the colors of the rainbow.
You'll need
- A clear glass of water (or a glass prism)
- A sunny window and a sheet of white paper
- A bowl of water and a pebble
- Optional: a white paper circle, crayons and a pencil to spin it on
What's in the book
Pages 33 to 41. Two ways to touch something far away (throw something, or send a wave); Newton's and Huyghens's ideas; light as tiny waves (fifty thousand to an inch) that take seven and a half minutes to come from the Sun; then a prism splitting sunlight into colors, and a spinning card of colors that looks white.
The lesson, step by step
Hook question
SayHow could I touch you from across the room without walking over?
Let your child try ideas. Buckley gives two: throw something at you, or shake the floor so a wave travels to you.
Read together
Read pages 33 and 34.
Thus we see there are two ways of touching anything at a distance; 1st, by throwing some thing at it and hitting it; 2nd, by sending a movement or wave across to it
Drop the pebble into the bowl of water. Watch the rings travel to the edge.
SayLight from the Sun comes to us in waves, a bit like these ripples, only far, far smaller and faster.
How small, how fast
Read the bits on pages 38 and 39.
So very, very tiny that about fifty thousand waves are contained in a single inch of space!
Well, these tiny waves take only seven minutes and a half to come the whole 91 millions of miles.
SayLight is the fastest thing there is.
Try it: a rainbow on the wall
Read pages 39 and 40.
Here at my left hand is the red, beyond it orange, then yellow, green, blue, indigo or deep blue, and violet, shading one into the other all along the line.
Set the glass of water on a sunny windowsill, with the white paper on the floor or wall where the light lands. Move the paper until a little rainbow appears. (A prism works even better.) Name the colors in order.
Safety: never look straight at the Sun, not even for a moment, and never through glass, a lens or sunglasses.
The idea in plain words
What are these colours? Do they come from the glass? No; for you will remember to have seen them in the rainbow, and in the soap-bubble, and even in a drop of dew or the scum on the top of a pond.
SaySunlight is all the colors traveling together. Water or glass bends each color a different amount, so they spread out.
Optional: color a paper circle in slices of rainbow colors, push a pencil through the middle and spin it fast. It looks pale, almost white. Buckley warns that it will look a little dirty.
Tell it back and check
Your child explains where the rainbow on the wall came from. Then ask:
1. Name the colors in order.
2. Is the color in the glass, or in the sunlight?
3. How do light waves get here: thrown like a ball, or passed along like a wave?
What we know now
Buckley says light waves travel in an invisible "ether" that fills space. Scientists later found there is no ether: light can travel through completely empty space. We also know light travels about 186,000 miles a second, and takes a little over 8 minutes to come from the Sun.
Afterwards
Notice it this week: rainbows in soap bubbles, a sprinkler, a puddle with a little oil on it, or a CD. With the Sun behind you after a shower, look for a real rainbow.
Tip
The rainbow is easiest in the morning or late afternoon, when sunlight comes in low through a window.
Answers to the book's problems
1. Red, orange, yellow, green, blue, indigo, violet. 2. In the sunlight; the glass only spreads the colors apart. 3. As a wave.
Worked out for this site from the scan. If a number in your copy differs, trust the book.