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Second day ideas about light

September 8, 2011

On the first day of our inquiry into light, students predicted what they would see standing in a room, looking into the hallway where a friend was shining a flashlight. There were many ideas. A big surprise for many students was that they didn’t see a beam.

So on the next day, I asked each research group to answer to following question

(A) Why didn’t we see a beam? What is happening that would explain why we didn’t see a beam?

(B) Is there a different situation in which you think you would see a beam? What’s going on differently in this situation that would explain why you would see a beam?

The main ideas that arose out this discussion were the following:

Idea #1 The light was too dim. A brighter light would allow us to see the path of light. Some said that maybe this is because humans eyes are only good enough to see the path for really bright beams. One group talked about how maybe a cat or a camera could see the beam. Others thought that maybe it’s not just the brightness of the like, but the kind of light–laser light, flood light, LED, etc.

Idea #2 The hallway (or box) wasn’t dark enough to allow us to see the beam. Some said that a darker room would allow us to see the path of light, because there would be more contrast between the darkness and the beam.

Idea #3 The hallway (or box) was too much of a closed space. A more open space would allow us to see the path of light, because there wouldn’t be any reflections (off walls) to interfere with the beam. The ideas about how and why reflected light interferes with the beam were unspecified, although the word destroy and mask came up

Idea #4 We couldn’t see the beam because we weren’t actually in the hallway (or box) where the beam was. Some said that whether you see the path of light, the source of light, or just lit areas depends on where you are standing and looking. There was a lot of discussion about whether there is a distinct boundary of the beam or whether it’s a “fuzzy” boundary or of it’s just a gradual dimming as you get farther from the center of the beam. They also discussed that a laser might have a distinct boundary while a flashlight probably would not.

Idea #5: The path of light is only visible when it hits something in the air (like moisture, smoke, or dust). What happens when light hits water droplets was unspecified, although the words scatter, reflect, and absorb came up.

They’ve been sent home to make observations that will help us to sort out these ideas.

I wrote in their homework the following:

“Your homework is to make some observations that will help us to sort out these different ideas and possibilities. You might experiment using brighter and dimmer flashlights. You might experiment shining flashlight in somewhat dark and very dark rooms. You might shine flashlights in small closets, in large rooms, and outside. You might shine a flashlight and stand in different areas to see if and when you see the beam. You might try shining some light through some smoke, dust, or fog. It doesn’t matter what you choose to do, but your job is to write a clear explanation of what you did and what you observed in a blog post. You will also need to read and comment on at least one other post. “

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2 Comments leave one →
  1. Andy "SuperFly" Rundquist permalink
    September 8, 2011 1:30 pm

    This is great, Brian. I really like the homework assignment, especially the forced blogging and commenting. What system are you using for that? Would you like outsiders to comment, too?

    Did any of the students talk about seeing the sun’s rays on partly cloudy days? I love how they look like they’re spreading but they’re actually parallel. I once saw a talk where a guy showed sun rays seeming to converge on a point. He explained that the sun was directly behind him when he took it. Then he talked about how railroad tracks look the same. Very cool.

  2. September 8, 2011 3:12 pm

    I made them get any blog and send me the link. I have each of their blogs on my reader; and all of their blogs are on my blog roll so that it moves most recent posting blog to top. Feel free to look around.

    I do eventually want outsiders reading and commenting. So far, they’ve only read a paper called, “The virtues of not knowing” and had to write a post about it. I do think that one purpose of blogs is to have a real outside audience, rather than a contrived one. I’m not sure when to do that just yet. Right now, I want to hold them accountable to each other–our ideas and feedback, before I ask them to be accountable to a broader community.

    I’m using their blogs ultimately as a stepping stone toward their “capstone” independent project and paper (needed to get an A). Everyone needs to write three posts about some independent observing and thinking they do outside of class.

    (1) A blog post about some physical situation or event that made them stop and wonder about it. [My blog post is an example of what they need to do for their first blogpost]

    (2) A blog post about some situation that made you stop and wonder; and some ideas you have about how to understand that situation. They can build off first or start anew.

    (3) A blog post about some experiment or new observation you made to help you sort out your ideas, including how your think changed as a result of the new observation. Once again, they can build off first or second or start anew.

    The idea is that this will turn into a deeper investigation they carryout. I wanted to provide some scaffolding along the way, and the blogging was the best way I could think to do this. I am now choosing to use it for other reasons, such as responding to a reading and reporting on at home observations.

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