Light Waves

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Objective

SWBAT describe how light can be reflected, refracted, absorbed, and that it travels in waves.

Big Idea

How does light travel?

Introduction

10 minutes

I began by having students write the focus question, "How does light travel?" in their science notebooks.  I drew a simple picture on the board (Light Review) and asked my students to draw it in their notebooks, and add arrow to show how the light traveled.  After a few minutes, I gave them time to discuss their pictures with a neighbor, and share what they found with the class.  This served as a review of yesterday's lesson (Ray of Light), as well as a way to reopen our discussion about whether light travels in straight lines or waves.

Engagement

30 minutes

I turned off the classroom lights, and took out a laser pointer.  I shined it on the wall, and we discussed how you couldn't see the light until it bounced off of something, like the wall, and into your eye.

I chose a student to come up to the front of the room, and hold a mirror at an angle (I put it at about 45 degrees from the front of the classroom).  I asked students to make a prediction about where the light would shine if aimed the laser at the mirror from the opposite front corner of the room.  Then I aimed the laser at the mirror (I told the student with the mirror to keep their eyes shut tight to build up a little drama), and turned it on.  I had them discuss what they saw at their tables, then share with the class.  They used the word "reflection," but if they didn't I would have drawn it from them.  I had them write "Light can be reflected" in their notebooks, and draw a diagram of how the light traveled.  I also had them write their own definition of "reflect" and add it to the index of their science notebooks.

Next I placed a clear plastic cup of water on my front table, and then placed a straw into the cup.  I gave them a minute to share what they saw with their shoulder partner, then asked them to try to explain why.  With an effort not to get overly technical, I explained that light moves at different speeds through different materials.  The light that is traveling through the water is being slowed down, which bends the light, making it look as though the straw is broken.  I explained that when light travels through something and the direction is changed, it's called refraction. I had them write "Light can be refracted" in their science notebooks, and write a definition of refraction, as well as write refract in the index of their science notebooks.  We drew a this diagram together.

At this point I went back to a demonstration I did yesterday, Scenario 2 from Ray of Light, which was shining a light into a box, because I didn't use the word absorb.  We wrote "Light can be absorbed." Again, each student drew a picture, wrote a definition, and added the word "absorb" to their index.

Finally, I wanted to provide my students with evidence that light travels in waves.  I turned the lights back off, and set up my laser pointer to shine on a single hair (Here are instructions from Student Science.)  I didn't get into measuring wavelengths with my class, but showing them the dark and bright spots did allow me to provide evidence that light travels in waves.  I kept my explanation limited to the idea that if light traveled in a perfectly straight line, the hair would just make a straight shadow.  I had my class write "Light travels in waves," in their science notebooks, and we drew this diagram together.

Closure

5 minutes

This was a vocabulary heavy lesson, so for my closure, I wanted to provide my students a little more time to work with the two more easily confused words.  I asked them to compare and contrast "reflect" and "refract," either in a sentence or using a diagram (a Venn diagram or a Double Bubble if your students use Thinking Maps.)