What is "Radiation?"
Lesson 1 of 17
Objective: Students will access prior knowledge about the concept of radiation as a way for us to frame the study of electromagnetics.
We begin a new semester and a new unit with today's lesson. Though the unit is called "Electromagnetics" I intentionally withhold the name from students. To address certain Physical Science standards, I want to focus our work on the concept of "radiation" and, today, I want to capture initial student ideas about radiation without the suggestion of "electromagnetics" influencing their thinking.
Indeed, the lesson begins with a free write in response to a prompt: "What comes to mind when I say the word . . . radiation?" I give students 2-3 minutes to write in their notebooks and urge them to keep their pens moving, even if their ideas start to wander.
After the free write, I have students engage in a "pair-share." They turn to a classmate and share their responses with one another. Having done so, they are much more likely to volunteer ideas in a large group.
After sharing semi-privately, I facilitate a round of large-group sharing. Students raise their hands to share a single idea at a time and I record their thoughts on the Smartboard. Many of the responses are centered on the concept of health concerns, a result I had secretly counted upon! In the next segment of the lesson, I provide students with a 3-page excerpt of an Internet article entitled "Cell Phone Dangers." We use this to begin the exploration of health hazards and radiation.
Cell Phone Reading
I provide my students with a paper copy of a short excerpt from an Internet article describing the dangers of cell phone use. The article describes a purported increase in brain cancer that can be expected and generally focuses on dramatic health risks that individual are subjected to when in the proximity of "microwave radiation" devices. I ask my students to highlight the paper copy of the article as they read. Before they read, I show them the protocol we will use to discuss the reading later in class.
I purposely choose an article that promoted the dangers of cell phone radiation for several reasons. First, students have heard the idea before and, as a unit goal, I want students to be able to evaluate claims of health risk associated with electromagnetic radiation (NGSS Performance Expectation HS-PS4-4). Second, virtually all students own a phone and, one assumes, they are emotionally tied to the outcome of this discussion. Third, despite my skepticism that there are any radiation risks associated with cell phones, I think it best that the students arrive at that conclusion for reasons other than my attitude.
On the other hand, by promoting this idea (that cell phones are radiation risks), students may believe that their cell phone is harming them for some time; they may hold onto this idea until we can build a deep understanding of electromagnetic energy and its ability to affect human health. While that concerns me, it is a fact that some students already hold that belief, yet continue to use and carry phones. In other words, this is not the first time they've heard this idea! Before the discussion ends, however, I do take some time to add some balance to the learning. I ask my students how long it would take to find an article that completely refutes this one. Their answer is "less than a second" and I take the time to warn them that this article should not be taken as the absolute truth and final word on the matter.
I give students about ten minutes to read and prepare for the discussion. When that time is up, I share a discussion protocol on the Smartboard and encourage a student-led conversation.
Discuss Cell Phone Reading
To process the reading, I use a protocol that allows students to unpack their thinking a bit at a time. It also helps to ground the discussion in the text and minimize the likelihood that students get carried away by the attraction of sharing endless personal anecdotes that are (maybe) related to the topics within the text. In the first round, students share portions of the text that they found intriguing while withholding personal opinion. Students piece together the important ideas presented in the article - in a sense, we extract the main messages of the text, without editorial comment, in this part of the protocol. In the second round, they are encouraged to infer, which opens up the discussion for more personal reactions. Here, students connect the text to previous warnings they've heard about cell phones, microwaves, and other purported health risks. Finally, a round of questions helps us to articulate the dilemmas that still linger.
Student speakers have a dual responsibility. First, they are sharing their ideas. In addition, they must be aware of others and be ready to designate the next speaker by yielding the floor. I participate occasionally but mostly monitor the conversation for clues that we are ready to move to the next phase of the protocol.
When the discussion is over, I ask my students to do two things. First, I want them to jot down three key questions about radiation that I have crafted. As they do so, I share with them that these questions are our guides for the next several lessons; no need to address these right now. However, I do ask my students to craft their own definition of "radiation" based on their previous knowledge and today's discussion. I urge them to keep this definition in a place that can be found easily; we will return to it later as a reference for our developing sense of the word.
If time allows, I ask students if they are willing to share their personal definitions with the class. I listen for commonalities and differences and try to make connections between student definitions.
To wrap up the lesson, I note that we have used a number of words that are essentially synonyms for one another: "radiation," "electromagnetic radiation," "electromagnetic waves". In addition, the ideas of x-rays, heat, microwaves, and radio waves have all been mentioned in our discussion. I tell my students that we have an organizing principle for all this: the electromagnetic spectrum.
I share a series of slides, with students taking notes (the entire slide show is made available electronically) featuring some simple aspects of the spectrum. In one slide, I show an image of a generic electromagnetic wave. In a second slide, I show the range of waves from radio to gamma-rays and stress that, for now, the distinguishing characteristic is wavelength. I point out the kinds of waves that have been discussed and identify the visible light portion of the spectrum.
As a final comment on the lesson: I note to students that we live in a sea of electromagnetic radiation - a word I use quite intentionally - from radio waves that fill the room, to the infrared waves each of our bodies emits, to the sunlight that streams through the windows. The obvious next step is for us to understand the conditions under which this radiation is and is not dangerous. The rest of of our work in this unit takes us in that direction.