ALEX Lesson Plan

Throughout this lesson, students will discover how the lens in your eye helps focus light. First, students will discuss the parts of the eye and how these parts work together to allow us to see. Then, students will use a clear plastic bag filled with water to create a model of an eyeball to investigate how the lens in your eye helps focus light.

This lesson results from the ALEX Resource Gap Project.

For the class:
magnifying glass
flashlight

For each student: 
copy of the Eye Spy lab sheet
science journal

For each group of students:
a zipper-style plastic bag filled with water (do not over fill)
mirror

Projector to display Eye Spy lab sheet

Individual devices to display Eye Spy sheet (if available)

Teacher background information: One critical component of the eye is the lens. A lens bends light. A magnifying glass has a convex lens, which bends light rays toward a common point. When you look at an object, light enters the eye through the lens, which is convex. The light is focused onto the back of your eye on a layer of light-sensitive cells called the retina. The retina then gathers the information and sends it to the brain to be processed into an image.  

Teachers will need to provide a copy of the Eye Spy lab sheet to each student or a digital copy on individual devices. The teacher will need to place students in groups of 3-4 for the lesson activities.

Students:  This is an introductory lesson. No student background knowledge is needed.

Essential Question:  How does the lens in your eye focus light?

Engage:  

Ask the question: How many of you have used lenses to see today?  Explain that if they have used their eyes, then they have used lenses because we all have a built-in lens in our eyeball.  Now ask, "What is a lens?" (An object that bends or refracts light.) Allow the students a few minutes to discuss this question with a partner.  Explain that lenses are found in many devices we use with our eyes.  Depending on a lens's shape, it can bend light rays to a point and bring them into focus, or it can spread light rays far apart.

Explore/Explain:  

Hold up a magnifying glass.  Explain that a magnifier is similar to the lens of your eye, except the magnifier has a hard, rigid lens, while the lens of your eye is soft and flexible.  Both lenses, however, are convex, which means that the sides are curved outward.  Convex lenses bend light toward a point to focus.

Darken the room and shine a flashlight toward a wall so that it makes a spot.  Invite the class to watch the spot as you place the magnifier in front of the flashlight.  Slowly move the magnifier back and forth.  The spot of light should get brighter and dimmer.  Explain that as you move the magnifier, you are changing the focal point of the light.  The spot will be brightest when the beam is in focus.  The light is focused onto the back of your eye on a layer of light-sensitive cells called the retina.  The retina then gathers the information and sends it to the brain to be processed into an image.   

Turn the lights back on.  Ask students to hold one hand in front of their faces so that they are staring at their palm.  Now tell them to quickly look up to the other side of the room.  Explain that as they change their view from near to far, their eyes adjust its focus.  Ask, "How do you think the lens does this?"  Allow a few minutes for the students to collaborate with a partner or group to answer this question.

Students will complete the Eye Spy lab sheet activity with a group of 3-4 students.  Each group will need a mirror and water-filled zipper bag.  

Elaborate:

Have each student complete the following journal entry:  Your eye has a flexible lens, much like the bag of water.  Based on your experiments, explain how you think the lens in your eye adjusts to change the focus from nearby objects to far away objects.

Formative:  The teacher should use the class discussions and teacher observations during the lesson as an informal assessment.  The Eye Spy lab sheet can also be used as an informal assessment.

Summative:  The students' journal entry should be used as a formal assessment: Based on your experiments, explain how you think the lens in your eye adjusts to change the focus from nearby objects to far away objects.

Accelerated students may write a journal reflection to answer the following questions:  What do you think happens to the lens in a person's eye over time?  How does this explain why some people need to wear glasses?

The teacher will need to pre-teach key vocabulary words to students that need extra preparation--lens, convex, focal point, and cornea.  Students may also need to be paired with a peer tutor or pulled to small group instruction for the Eye Spy activity.