“But We Were Told Light is Waves”

It’s amazing what some students have heard and believe on “school faith.”

As the first activity in my Physics 2 class we do the Pinhole Camera with a light bulb and view the image on a screen. The first day I showed the class how to create a simple pinhole camera out of a box and some aluminum foil (if you want to see what mine look like let me know.) This year I rewrote the lab to be totally inquiry based. They made a number of general observations and wrote 7-10 “I wonder…” statements or questions, they then experimented and tested their “I wonder…” statements and made observations. This rewrite to an inquiry lab was great. All of the groups wondered about and tested the same things I had on my previous version of the lab (move the screen, move the bulb, make a bigger hole, make multiple holes, use two bulbs, etc). So that part of this process was excellent.

The next day after a brief discussion about some of the observations we saw I instructed each group to create a model on a WB for the situation. I reminded them that the model should be simple, but yet be able to explain ALL of the observations they made. Here are two of the models I got:

Pinhole Model 1

Student justification: “Light travels in waves”

Pinhole Model 2

“I was told light is a particle that travels in waves.” Thus the dots in wave form here. I find it interesting that the waves keep getting bigger. The student had no particular explanation for that, just that they were waves.

I keep trying to ask “what about this lab shows that light travels in waves?”

“I don’t know, but it does.” was a common response.

It took myself and another student group about 20 minutes to finally convince the bottom group in particular that we don’t need to model the light as waves. And even now I’m not sure if they bought it or just wanted to be done with the conversation so they gave up.

“Why can’t we use straight lines.” another group said. Their board did show a linear model for the light, and they had the arguments to back it up.

“We have no evidence to back up the claim that they are waves.” I said. “Straight lines explain the behavior and it’s a lot simpler to use then draw crazy wave forms.”

I went on to say that “we haven’t “disproven” the idea of light as waves, but we surely haven’t proven it. Science comes with the burden of proof.”

So as I analyze this class discussion a couple of questions come to mind:

1) Do other modeler fight this battle of using a model that we have evidence for vs. what they have been told. (I find it A LOT in chemistry too, especially with the atomic model)

2) Was this a lesson for my students about science at its finest? Did I end the discussion too quickly because I wanted to “keep moving?”

3) Should I let them use their mental model until it totally breaks down and/or becomes too difficult to use?

If you have any answers or thoughts about these questions, please comment below.


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