Making a Water Lens

This lesson developed by Reach Out!

Recommended Age Group: Early Elementary, Later Elementary

Guiding Question

  What is a lens and how does it work?

Objectives

Concept:

A lens is a curved piece of clear glass or plastic used to focus light.

Facts:

We can think about lenses by comparing facts about our eyes:

• Nearsighted people have eyes that are too long from front to back.

• Farsighted people have eyes that are too short from front to back.

• Convex lenses help eyes to focus up close.
• Concave lenses lessen the power of eyes so they can focus on things far away.

Principles:

• Refraction is when a beam of light changes direction.
• Convex lenses curve outward in the middle.
• Concave lenses curve inward in the middle.

Skills

• Observation skills
• Making inferences
• Drawing conclusions

Materials

1. Clear plastic wrap
2. Newspaper
3. Water
4. Teaspoon or eyedropper

Room Preparation

Students need table space and elbow room.

Safety Precautions

None.

Procedures and Activity

Introduction

1. Ask, “What is a lens?”
   
   Review concept of a lens being a clear piece of curved glass or plastic.
   
   
2. What does a lens do?
   
   A lens focuses a beam of light.
   
   
3. Today, we are going to make a water lens and learn how lenses work.

Activity

1. Lay a page of newspaper on desk or tabletop.
   
   
2. Lay a piece of clear plastic wrap on top of newspaper.
   
   
3. Put drop of water on plastic wrap.
   
   
4. Observe the shape of the water drop.
   
   
5. Look at how the newspaper print appears under the “water lens.”
   
   
6. Why does the print appear the way it does?
   
   
7. Add more drops of water. Note the shape of the water and how the newspaper print appears.
   
   
8. What is happening? How might this knowledge be useful?
   
   
9. Talk about nearsightedness and farsightedness. Share information about bifocals, where the top lens is for distance and the bottom lens is for close-up and reading. Relate to water lens.

Closing - Original Question

Ask again, “What is a lens and how does it work?”

Is a water lens concave or convex? Review these terms and find a water lens is convex—it curves out in the middle. A convex lens helps our eyes to focus close up.

Evaluation

Have students share out loud what they have learned about lenses and focusing light from doing this experiment.

Have students help other children do this experiment. Listen to them for evidence that they understand the concept of a lens, the principles of refraction, and the difference between concave and convex lenses.

Extension Ideas

1. Invite an optometrist, ophthalmologist, or eyeglass fitter to come and share more information about lenses, eyes, and glasses.
   
   
2. Get some convex and concave lenses from a a toy store or science supply shop. Experiment with looking at different objects with these lenses. Write down what you see and why you think it happens.
   
   
3. Think about the variety of uses of lenses—for studying insects, making and using microscopes, helping eyes see, astronomy and telescopes, binoculars....

Careers Related to Lesson Topic

• Astronomers
• Doctors
• Eye glass fitters
• Jewelers
• Lens makers
• Ophthalmologists
• Optometrists

Prerequisite Vocabulary

Farsighted

Eyes that are too short from front to back. This means that the person can only read things from a distance.

Focus

Bringing light waves to a point and helping something appear clearer and sharper in detail

Lens

Clear piece of plastic or glass that is curved to help focus beams of light

Nearsighted

Eyes that are too long from front to back. This means that the person can only read things that are up close.

Refraction

The change of direction of a beam of light