Lesson 7 of 11
Objective: Students learn how light waves bend differently in different mediums.
I started this lesson planning that it would be about reviewing our understanding about how we perceive light and touching upon the concept of refraction. So I held up a water bottle from one of my students, that had a straw in it. The top of the straw looked smaller and the rest of the straw in the drinking water looked bent. I asked students to look at the water bottle carefully and tell me what they noticed. They mentioned that the straw looked like it was bending and the obvious difference in the top part.
I asked why they thought it looked that way? Their answers varied with many ideas that really did not have anything to do with light. They referred to it as an "optical illusion."One student said, "The straw looks bent because that's the way we see it."
I said that it was close! I explained that the illusions are because of the way our eyes have light entering into them. As I probed them with more questions about it, I realized I needed to take a different direction and that this lesson was going to transform into simply a lesson about refraction! I switched gears last minute!
I believe being a responsive teacher to the needs of students is extremely important in teaching inquiry based science. If I didn't change gears and act upon this opportunity, the standard would not be mastered at the levels that these students require. At this grade level, this is key so that they build their foundations correctly for future science study! I now needed to think quickly and gather materials on the spot!
Materials on the Spot! Water, beakers, tongue depressors ( pencils or rulers will work too), iPads and Science Notebooks)
I quickly responded by thinking on my feet about what I could do to really drive home the understanding of refraction. I asked them to grab their notebooks, iPads, and pencils. I quickly grabbed a bunch of tongue depressors and we headed to the lab. I wrote the word "refraction" on the board and the Driving Question: How does light energy bend?
They sat down in their table groups as I filled up 5 beakers with water. A student passed out the tongue depressors. (I will call them sticks, for comfort's sake. Somehow, "tongue depressor" isn't as fun.) I asked them to tell me what they thought the Driving Question meant? We discussed what they thought they knew and I could assess that reflection was the only concept they had of how light energy is transferred because they can take their iPad in the middle of the afternoon and bounce light rays from the window to the ceiling in our classroom!
Next, I asked them to place the stick in the beaker and sketch exactly what they saw in a fresh page of their notebook. Writing descriptions in their notebook and sketching needed to be coached a little bit as I reminded them about accuracy skills. They photographed the beaker, zoomed in the photo and looked at it using their iPad. Most did this voluntarily and it really helped the sketching. One student made the connection that it looked like a platypus tail, so I questioned and coached for more precise descriptions. I also prodded them to think about why they were seeing what they were seeing? "How do you think light energy is being bent?" Some concluded that it was an optical illusion and seemed satisfied with that. They avoided the idea that light direction was being changed even with my prodding. One shared that there was magnification of the stick like the inquiry we had done by filling a plastic bag with water and looking through it. They were getting closer, but I pushed with more questioning: "How does an optical illusion occur?" They were completely stumped. I asked students to explain. From those explanations, I coached them to be more accurate in their understanding by looking up refraction and doing a little research on their iPad.
My students weren't grasping this! They referred to the idea of reflection at this point, even though they had looked up the word refraction and I had visited to discuss their understanding. I brought up a video that I thought would explain it well. I asked them to take some more notes underneath their drawings as the video played. This video was the most appropriate illustration for fourth grade level that I could find, without delving too deeply. I was looking for the simplest concept of bending light rays and how it creates displaced looking images. The narrator is a little hard to listen to, but I stopped the video and clarified every step of the way. When it introduced the activity, I jumped on the opportunity to do another activity.
After the clip, I quickly gave each table team a coin to place in the bottom of their glass. I suddenly heard a chorus of amazement! I continued to probe with questions about what they thought was going on. The floating coins just blew their minds. They had never noticed something like this before! As I visited one group they tried to explain how it is layered, but could not connect the idea of refraction yet.
I needed to change gears again! I got out a bottle of oil. I poured a small jar of oil and called my students to the counter since I didn't have enough oil to go around the groups. As I held the oil up, I asked students which liquid they thought was thicker? They didn't know.
I asked them to come to the counter and gently stir the water and oil in the two containers and shut their eyes to compare. Some thought the oil was thinner and I had to work with them to see the viscosity of the oil. "Oil is thicker!" was finally the conclusion. I wrote the word "viscous" on the board and explained that it referred to the density or thickness of the oil. One by one students tested the oil and water to feel it. Now they were ready to look at objects in the oil and make new observations!
An Oily Difference
Adding the oil to the mix of understanding refraction opened up a whole new understanding again for them. I questioned my students during their observations, pushing them to think about the oil and comparing it to the water. How did the objects look different? Why did the oil change the look of the objects? Was it layered anymore? Some of my students really wrestled with why the stick in the glass looked "fatter" and tried so hard to make sense of things as we discussed the differences in the way the stick looked and why the coins don't look like they are floating anymore. To add another twist to the whole investigation, I poured the oil on top of water in a beaker and inserted a stick so they could see the differences together. Some students were now wondering why the oil floats on top of the water, extending their thinking again and helping them realize that the liquids had different densities. One student connected her experience from the year before when they did tests on different viscosities of liquid.
As we concluded our observations, I realized that this concept was much more difficult for most of them than I expected. I also realized that this lesson is an important investigation to help them deepen their understanding of how light waves work. It laid the foundations needed for them to understand how we perceive light in order to fully understand the standard.