Ray of Light

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Objective

SWBAT describe how we perceive things through sight by explaining how light is reflected from an object into our eye.

Big Idea

How can we model how we see things?

Introduction

10 minutes

I began by having students write the date and the focus question, "How can we model how we see things?" in their science notebooks.

Under this question, I asked them to explain, through words and pictures, how we see things.  This is an intentionally broad question because I want it to be accessible to my students with the least prior knowledge. After a few minutes, I reminded them of our expectation to speak and listen respectfully, had them share their ideas with their tables.

Engagement

30 minutes

I structured this lesson by beginning with very simple scenarios involving light and vision, and made each situation increasingly complex.  After each scenario, they were to draw how the light travels.  I gave my class a great deal of support in the first scenario (we worked on it as a class, they copied it into their notebooks), and gradually withdrew that support until #5, which they completed independently to see if they could apply their knowledge to a new scenario.

  1. I turned off the classroom lights, and turned on a small flashlight pointing up.  Students agreed light traveled from the bulb, into their eyes, and that it traveled outward in all directions.  A student disagreed that the light traveled out in straight lines, and suggested light traveled in waves.  It does travel in waves, but I didn't want to just tell them something without empirical evidence, so I told them they could choose how they would represent the light rays in their drawings, either straight beams or waves.
  2. The next scenario I set up was to shine the light into a box so that they couldn't see it.  This established that light could be absorbed, and that you cannot see light if something is in between your eye and the light without something to reflect the light to you.
  3. I drew a picture on a sticky note and placed it at the bottom of the cardboard box.  I then pointed the cardboard box at each of them from the front of the room.  Because the box was dark, most students couldn't see the picture.  The reason for this scenario is to show that when there is no (or not enough) light on something, we are unable to see it. 
  4. This was the same set up as 3, but I shined a light into the box.  This is the inverse of 3, when light shines off of something and into our eyes, we can see it.

Assessment

5 minutes

Finally, I showed my class Scenario 5 Illustration and explained the following situation:   You're walking down a street late at night.  There are no lights nearby, but the moon is out.  If you were walking under a tree, and couldn't see the moon, but there was a sign just past the tree, could you read it?  Why or why not?