Who Turned Out the Lights?

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SWBAT develop a model to describe how light reflecting on an object allows us to see the object.

Big Idea

Students use lines, rays and diagrams to explain how light rays reflecting on an object help us see the object.

Warm Up: Perspective of Inside a Lion

5 minutes

The learning goal today is to build on understanding of light and how it is transferred from place to place. I want them to understand a variable that changes light, helping them to understand that reflection of light on an object is necessary for us to be able to see an object. 

I opened this lesson today with a poem from Shel Silverstein: It's Dark In Here.

The poem begins by saying " I am writing these poems from inside a lion, and it's rather dark in here. 

I asked my students if they had ever tried to write in the dark? Had they ever tried to read in the dark? Had they ever experienced complete darkness? What does it feel like? What do you sense?Why can't we see at all in complete darkness?

I got varied answers that were basically "because it's dark." From this, I could see I had a great base to build upon today as it gave me the context of their levels of understanding. No one said anything about light waves or reflection at this point.

I asked them if they were afraid of the dark? We shared ideas about how in the dark our mind plays tricks on us through our eyes. Through these remarks, I could see that they understood that in darkness, our eyes see a little bit of light or that because we cannot see, our eyes do things and we might think we see objects a certain way. One student shared how the door in her bedroom looked like a monster in the darkness because of the wood (grain).  We discussed how our eyes adjust to the darkness and we can see in our bedrooms after the lights are out. 

Students at this point had a good foundation for us to be moving forward as we continued using lightening to examine how light travels.

Let's Look at Lightening!

5 minutes

This short video is a compilation of lightening striking and we can hear the thunder after the strike. Watch it to 1:38 and then stop. The screen is black. I begin to open the discussion at this point. 

I asked my students to note in their notebooks to describe how completely black the screen is. I continued with more questions to build understanding: If we stare at the screen, do you think we will be able to see anything more than just the black? Why or why not? ( Sometimes students think if you stare long enough into blackness, our eyes will adjust and then we will see. I explained that is only true if there is even the tiniest of light sources.)  Then, I clicked play. The lightening illumined the lightening rod and we could see in a moment what it is striking. I replayed it in order to help them understand completely the connection between darkness and the absence of light related to the fact they can't see anything until the light appears.

I asked my students why can we see objects light up in lightening storms? They talked about various properties of light and how it worked. Some students had questions about lightening that I asked them to write down in their notebook. One in particular I chose to answer later after the investigation. This student wanted to know about why the lightening is first and the thunder is second? Another student wanted to know why thunder exists? I started to question them about what they know about sound and we began to formulate our own understanding of vibration and how the lightening must create a vibration as it travels through the air. I shared with them that when electrical transformers blow up, there is a big bang. I told them that it is the electrical energy that is responsible for the sound, but that we should research more about it. I also said that the former question would be answered after the investigation. 

My students have begun to grasp the understanding and joy that science questions can be answered as we go along and that the teacher will guide them to find the answers rather than just give them answers.

I continued to support their inquiry and ask if students have any other questions that would help them understand this idea better. Finally, I asked for any "aha" moments. Was there anything that they never thought about before? Some shared that they never thought about that they could see more than just the lightening when it struck. They also discussed that the sound was after the lightening and made remarks about how different lightening can look. When they were quiet, I knew it was time to move them into the lab for some fun with flashlights and darkness.. 

I told them that the next steps in the investigation would probably answer our Driving Question about light. I wrote it on the whiteboard in the science lab: How does light travel? 

Mirror Mirror

20 minutes

Materials: small mirrors for groups of three or four, flashlight, iPad or movie device.

Today's short investigation will help students really understand that reflection is the bouncing of light rays. In yesterday's lesson, they explored it using a Mira, which is fairly transparent. Now, they are using a reflective surface. They also will discover that all surfaces reflect light and that reflection is part of being able to see.

I turned off the lights in the lab and shut all of the blinds so that it would be as dark as possible.

I asked a student to shine a flashlight on a bare wall starting from right in front of the wall so the round beam of light was visible. Then, I had him step backwards to the longest distance across the room. The student moved backwards until we couldn't distinctly see the light anymore. I moved him forward so that it would return and we took a measurement of 7.5 meters. I asked them to note it in their notebook.

Then, I gave two mirrors to two students and placed one of them at the distance that was measured and one against the wall. The same student shined the flashlight on one mirror so that the beam bounced off it and into the other mirror. Students gathered around to see what was going on and the strategic questioning began. What do you notice? Why to you think this is happening? I asked them to measure how far the light had to be away from the mirror before we could see the reflection on the ceiling. We measured 1 meter. The measurement difference was to show them that the light would bounce at a fairly close proximity.  As the student moved around, we could position it so that the light kept bouncing here and there. I started to really push out the questions. I pushed them first to explain why light is brighter in the mirror? They grasped this so quickly!

We continued to listen to each other talk about what we thought was going on. I kept driving the discussion using questioning that got them to think about how light travels. When we shined the light on the wall, what happens so that we can see it on the wall? When we shined it on the mirror, what happens? Why does this happen? One student was able to easily explain how it bounces back and forth. 

They had a lot of trouble with trying to understand how the light is diffused when no mirror was present. So, I had to explain it again through questioning. "Why did it get dimmer the farther back he moved? What does that say about how light travels?" They still couldn't get it. They did understand quickly that the mirror bounces light off of it, but could not quite get why the light would be stronger as they squinted and covered their eyes as it blinded them. 

I asked them to note what they saw in their notebooks in order to keep record of their ideas and thoughts. I posed the Driving Question once again: How does light travel? And then, I asked how they knew? "It's the material that makes the difference," was one reply. But even with my prodding and continued response, they weren't getting it! This is the most difficult concept, yet so important to master the standard fully! 

Using this Phenomena to Understand How We Use Light to See

20 minutes

After we returned from the lab to our classroom, I wanted to address my student's excellent question about why we hear thunder after the lightning.  I asked, "Based on what you have already observed, does sound travel faster than light?" Sound is faster, was one reply. We also started to discuss how they thought light traveled. One student shared his explanation of his idea of light waves from some reading he did. I explained that light waves are made up of different components that can be pulled apart. I touched upon the idea that prisms can show us how light can be separated into colors, like a rainbow. The drawings he saw showed the waves as curvy as a sound wave. I really wanted them to focus on the direct light and how it travels in straight lines. 

So, to put to rest any misconceptions, I explained that light travels at 300,000 kilometers or about 186,000 miles per second. We looked at the clock and watched a second. Sound only travels about 300 meters per second. That is why you see the lightening before the thunder. I asked students log onto Kids Health website on their iPad to study the parts of the eye. Using this website, I had them do partner work to create individual drawings of the eyeball and labeling the parts showing how the light enters the eye. This helps them get ready for their assessment where they actually create a model eye and demonstrate that they understand how we need light to see.

Wrap Up With "The Dress"

10 minutes

To wrap up the lesson, I asked students to quietly write down their thoughts about what they observed. They really couldn't take many notes in the dark! So, this lesson was mainly interactive discussion about their observations. I quickly roved the class, scanning the notebook notes and could see they were struggling.

 Instruction of the phenomena:  I had to instruct how light travels in straight lines UNTIL his hits something and reflects or bends back. I explained that they were right that the light in the mirrors get brighter because the reflection is bouncing back and forth.

And then I asked that  we repeating our understanding. They said out loud that light travels in straight lines and that it can bounce or reflect. As I pushed for the close, I decided to bring up the current infamous dress that had been all over social media.

I brought up the dress on the SB and asked then what they saw. They broke out in all kinds of talking about the colors they saw. Black and blue, purple and orange and also white and gold. 

I had them break into groups as I repeated the colors they were telling me. Most saw black and blue. I still see white and gold and had three students with me. Two saw purple and orange. I hadn't heard that one before and it really baffled me.

I asked if light was involved in affecting how we see the dress? One student explained that he knew it had to do with photography and light. I explained a little bit about rods and cones in the retina, so they could understand that our individual eyes are made up from person to person a little differently. It helped them to understand that these differences make us see light or perceive color a little differently under certain circumstances. I brought up images that are used to test color blindness and we talked about each one. Certain students couldn't see certain images in blues and greens. I explained that is where the term "color blindness," which is very common, comes from.

As we closed the lesson, I emphasized again that light energy traveling and reflecting is necessary for us to see. That's why our eyelids are like window shades!