This lesson is designed for middle school aged students. I teach it to my seventh grade students in Central Massachusetts.
A newly added component of our Massachusetts state standards (part of the Next Generation of Science Standards, or NGSS) is waves and digital signals. A lot of teachers I have talked to do not like this aspect of the new standards since it is such a difficult thing to both show and explain. I honestly love it since it opens up discussion for so many things that are seemingly invisible to us yet so important. With nearly everyone carrying around smart phones it's a shame that so few people understand the basic functions that are necessary for the device to work. So much of it goes back to understanding both digital and analog signals and the bet place to start is a simple discussion of analog waves.
With the first of these two activities, students are challenged to complete a number of laser maze challenges using reflective-backed cardboard, a target, and a laser pointer. The second activity involves using color-changing LED lights to demonstrate how reflected light is perceived by our eyes. The best part of this activity is that it is fun, fast-paced, and completely blows the kids minds!
Prior to these two activities we spend a few days exploring basic wave structure and function and even discuss the myriad wavelengths of the electromagnetic spectrum. So, students are coming into this activity with some prior knowledge. The purpose of this activity is to show students how electromagnetic energy, traveling in the form of a wave, can be reflected, refracted, transmitted, and absorbed. Students complete two interactive and hands-on activities during one 50 minute class period. You will need some basic materials to complete the two activities as listed below and please feel free to use the documents I have made by accessing them in the links posted in the supplies area.
Laser Maze Supplies (groups of 2 - 4)
Challenges(posted on board or printed one per group)
Laser Pointers (1 per group)
Targets (1 per group)
Reflectors with little binder clip stands (at least 10 sets per group)
Convex Lenses (2 per group)
Colored LED Exploration (groups of 2 - 4)
Colored Circles Printout (1 per group)
Fluorescent highlighters (1 per group)
Step 1: Setting Up the Laser Maze Challenges
The goal of the laser maze challenge is to demonstrate the simple premise of light reflection, refraction, and absorption. As mentioned earlier, we used a number of previous resources to give students the full spectrum (sorry for the pun) of information about waves. We then discussed how color is simply a wave at a specific frequency. Check out this TedEd video about color.
Put the challenges up on the board or print them off to share with each group (CID stands for change in direction by the way). Tell the students that they are to complete each challenge in numerical order and once they reach a challenge involving lenses they should get your attention and you will give them to them (this is to prevent accidental breakage of the lenses). I first demonstrated the idea of using the reflective material to reflect the light from one area to another. I also showed them that the reflective material adhered to the cardboard is less then perfect and does not produce a perfectly reflected laser "dot" like a mirror does. This, at first, seems like a pain in the rear, but what it actually does is gives the kids a better chance of succeeding as long as they are working over short distances. Since the light is reflected in a kinda "blob" formation it gives it a better chance of landing on the target. Then again, the main reason I am using reflective mylar attached to cardboard is actually because it is impossible to break if they drop it unlike mirrored tiles or circular mirrors. With an actual mirror you will get a much clearer reflected light and ultimately will be able to reflect the laser light over a longer distance. You can see a couple of plastic stands and circular mirrors we used as a whole class demo in one of the pictures above.
I was able to secure the mylar from a local manufacturer that gives away short rolls and extras but you can buy it from a number of places (here is a link to one such location). I adhered the mylar to cardboard but I think it would be best if you actually adhered it to card stock that is nice and smooth. I actually have so much of this stuff that I will end up redoing it next year with the card stock. We used small binder clips as little legs to prop them up and attach them to books and what not. As for the lasers, any laser that produces a nice bright light will be adequate... just warn the kids that even though they are low class lasers (class IIIa) they still can cause eye damage. I had to read the riot act to a couple of classes but overall they really were well behaved (like a bunch of kittens with the darn lasers!).
Step 2: Making Laser Mazes!
Once you have the challenges posted you can start to distribute the supplies. Each group will need the following to start:
- At least 5 reflectors and binder clip stands
- One target
- One laser pointer
Tell the kids to work in numerical order down the list of challenges and to get your attention when they complete each challenge so that you can check if they actually did complete the challenge before moving on to the next. The easiest way to check if they have light reflecting from one reflector to another is to use an index card to block the light from each reflector. If the light no longer shines on the target when you block a reflector you know that the light is properly being reflected from that particular reflector. If the target is still lit up after blocking the reflector you know that the light is actually coming from a different reflector. Once the kids have worked through the first couple of challenges they can go up and get additional reflectors. You can give them the convex lenses once they complete the fourth challenge.
I typically will dedicate half the period to this activity. At this point the kids who have a tendency to lose focus are just about there and it's best to wrap it up and summarize before the activity loses its luster. To summarize I typically ask the kids a few different questions such as:
- How many challenges were you able to complete?
- What was the most difficult aspect of this activity?
- How could we improve the laser maze? New materials? Better materials? More time?
- How does the light energy travel from one reflector to another? (reflection)
- If we wanted to send a signal using light energy further, saw a mile away, what things would we need to improve to send a signal?
- What if we wanted to send the signal to the moon? How could we send that signal?
Step 3: Setting Up the Colored LED Adventure
The second activity draws on the same principles as the first and focuses in on reflection yet again. This time, instead of reflecting laser lights, we are going to see the effect of reflected colored light on other objects. You will need to print the colored circle sheet provided at the start of the Instructable, one per group. I attached my clamp lights on a pull down overhead screen but you can use pretty much anything that allows the lights to project light throughout the majority of the room. Before you clamp your lights on you should install the color changing bulbs and check that they all work. You get a remote for each bulb that you purchase but you can use one single remote for all of the bulbs so that you can nearly change all of them at once. You will need to get your room as dark as possible to make this work the best. I not only dropped my shades but also taped them to the window and blocked the light from my door since I have a glass window in the door. Get the room as dark as possible! Once you are set you can turn on your lights and make sure that they all change color right around the same time... you are ready for a strobe-light party now!
Step 4: Testing Out the Colored LEDs
Make sure each group gets a sheet with the colored circles and distribute one yellow fluorescent highlighter to each group. I had kids make an "X" on the top of one of their hands with the highlighter while I had the white light on. This is up to you and if you feel uncomfortable with them writing on themselves you can use a piece of paper in lieu of the hand... but it is really cool for them to have it written on their hand!
I then have the kids point to a green circle on the paper and a red circle on the paper then turn the lights to all red. The red circle will appear to be a lighter red color while the green circle will appear nearly black... this will definitely impress the kids. Tell them to look at their "X" and they will see that it is nearly invisible. Next change the lights to all green and the kids will see the green as a bright green and the red as nearly black and once again the "X" will be pretty much invisible. Finally, change the lights to blue and they will see both the red and green circles as nearly black and the "X" on their hand will glow brightly due to the fluorescence of the highlighter interacting with the blue light wavelength. At this point I use both the strobe function and the fade function on the remote and you get a really cool light-changing party going on in the room (check out the video at the start). This will all take about 15 to 20 minutes and will get the kids good and excited. You can have them write cryptic messages with the highlighters on paper or find objets of pure colors (i.e. a red ball) to see how they behave under the different colored lights.
At the end of the presentation I usually follow up with a number of questions:
- Why did the red circle appear black under the green light?
- Why did the "X" appear so bright under the blue light?
- What would happen to a banana under the blue light?
- What does this all have to do with reflection?
I can tell you that the kids were talking about this all day in school and kids came into the class excited about "the cool lights and lasers" that they were going to learn about. It's the end of the school year, June 5th, and I have kids excited about learning... priceless! I hope you give this a go and have as much fun as we have had with the lesson!
This is an entry in the
Classroom Science Contest