Week 16 - Light Behaves in Predictable Ways

Lesson 5
Lesson 5: Lenses Allow us to See New Worlds
Science In Action
Read pages 204 - 211 and make notes in your notebook.

Now that we've learned the scientific principles of refraction, we are going to study how these principles can be used to make our lives better.

In the last lesson we learned that as light passes through materials of differing density it refracts and moves in a slightly different direction. This knowledge has allowed us to build devices which enhance our lives. Let's examine some of them.


A lens is a curved piece of material, usually glass or plastic, which refracts light and causes it to bend. There are two basic types of lenses: convex lenses and concave lenses.

The Convex Lens

A convex lens is fatter in the middle than at the edges.

When light rays passes through a convex lens they come together, or converge, at some point. The place where they cross each other is called the focal point. By making the curvature of the lens larger or smaller you can change the focal point of the converging light.

Many lenses have convex shapes on both sides of the lens. These are called double convex lenses. Because the light crosses over at the focal point, the image becomes inverted (upside down).

The distance to the focal point focal point depends on the distance from the object to the lens. 

Did You Know?

What is the biggest lens you can think of? A large telescope perhaps? How about a lens made from groups of galaxies! That's right - galaxies. The lenses they make are called gravitational lenses. If you would you like to know more check out the following websites

See a larger picture.

Scientists use gravitational lenses to find the oldest stars in the universe.

The Hubble space telescope has recorded 10 gravitational lenses.

The Concave Lens

The concave lens is opposite from the convex lens in just about every way. A concave lens is thinner in the middle than at the edges. As light passes through the concave lens it diverges (spreads out). There is no focal point because the rays will never meet.

The Human Eye

Each of your eyes has a convex lens in it. The lens of your eye allows an image to focus on the retina (on back of your eye). But this living lens can change shape. This allows it to focus on objects near and far away. Muscles in your eye relax and contract to change the shape of the lens.

The lens is the white oval
in this picture.

But if the lens of the eye is so flexible why do people have to wear glasses? In the following activity you are going to conduct a small research project to answer that question. You will find your information on the Internet sites indicated in each question below.
Exercise 2.1: You're the Eye Doctor


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