Did you ever put a pencil into a clear glass of water and look at it carefully? Did it look as if the pencil bent or came apart where it went into the water? You were seeing an example of ,begin bold,refraction,end bold,. The pencil wasn't bent, but the image of it was.

The images we see come to us in light waves. Light changes speed slightly when it goes from one transparent material to another—from air to water, for instance, or from the air to your eyeball. The difference in speed changes the direction of the light waves, a change called refraction.

,begin bold,Lenses,end bold, are transparent materials formed with at least one curved surface. Lenses refract light so that an image is focused smaller or larger, depending on the shape of the lens.

A ,begin bold,concave,end bold, lens is thinner in the middle than at the edge. It spreads light waves out as they pass through it. Microscopes and magnifying glasses use concave lenses. They refract light into larger images.

A ,begin bold,convex,end bold, lens is thicker in the middle than at the edges—curved out, like the surface of our eyeballs. Convex lenses bend light waves together, focusing them to a point.

Your eye is much smaller than the things it sees. How can it shrink all the light from all the objects around you down to an image that will fit into your head? The convex lens in your eye bends the light waves, concentrating them into a tiny image on the retina behind your eyeball.

Question
Why do some words in the passage appear in bold letters?

Answer options with 4 options
1.
Bold print makes the text more interesting to read.

2.
The words in bold are defined in the text.

3.
The words in bold all have the same meaning.

4.
Bold print indicates words that are from other languages.