Arrival Craft: Use numbered axes to make a curve out of straight lines.
Use grids to expand pictures.
Introduction: We’ve looked at light before when we built periscopes and saw how light always travels in straight lines. Today we’re going to look at how light can be bent.
Individual Task: Lay a piece of clingfilm on top of some paper. Carefully put a droplet of water onto the clingfilm.
Look at text through a droplet of water and see how the water magnifies the text.
Gather Together: Light bends when it passes through a different material because light moves at different speeds in air and water (or in air and glass).
Set up ray box, show how a lens can bend light and move the focal point. This is how glasses and contact lenses work to help people see.
We can see how that works if we pretend to be light.
Get six children to stand in a line holding hands. They should walk forward taking the same size steps. They will walk from one side of the room to the other and stay in a straight line.
Then put a masking tape line diagonally across the floor. As they cross this line, the children must begin to walk in tiny steps, only a couple of inches at a time. Since the children will not all cross the tape at the same time, some of them will slow before the others and their line will bend.
That’s how refraction works! It’s also why light doesn’t get refracted if it hits the glass straight on, e.g. coming through a window.
Break for drink and snack.
Second Part: Lenses allow us to focus light where we want it, we can use that to correct vision problems, but we can also use it to make microscopes for seeing tiny things or telescopes for seeing things that are a long way away.
Individual Task: Making telescopes. There’s an amazing website that sells a whole range of telescope-making kits, they’re great value and really awesome! AstroMedia