Starting this week I felt like my students needed more practice constructing models and clarifying field lines, so we began the week by looking at iron filings and a magnet. The students had magnets and a sealed bag of filings and had to use both to try to model the magnetic field around one magnet and then when both were interacting.
To give them some guidance I showed the groups a demo I have that shows the magnetic field of a magnet pretty clearly with just iron fillings.
It is a plastic bottle, to which I added iron fillings. Then I glued a test tube to the top. To the test tube I added a cow magnet (which is the magnet I could find that best fits in the test tube). It is not a very strong magnet, but to show the field that tends to work best. I've tried a similar setup with a bar neodymium magnet with a 75lb pull and it worked, but the stronger pull made the field lines if anything less clear.
We then moved onto the rotation lab, it went fairly well, though I could not get the balloon/plastic bag flyer activity to work, it would repel from the balloon, but would just either stick to my hand or fall the the ground. So, instead I replaced that on the worksheet with the Van de Graaff generator demo and had the students write about their observations with the generator.
The actual demos I do with the generator are rice crispies on top (which fly off due to the buildup of negative charge in them), paper hair (which is just thin strips of paper tapped in the middle like the spokes of a wheel, this lets you both see repulsion and attraction when you bring the discharge wand close), and then student hair (I also have a wand with metallic strings that shows the same thing for students with short hair). All of the demos are the basic idea that like charges repel and opposite attract.
While the demo is certainly not necessary, I think it is really worthwhile to include if there is the one time budget money for it. The supplies I use are:
Van de Graaff Generator
Discharge Wand
Static Hair Wand
It is worth noting, for anyone that hasn't used a Van de Graaff Generator before that how well it works depends greatly on the weather that day.
We ended the week starting our models on how potential energy relates to the orientation and position of the objects, most importantly the distance between them. Continuing my thoughts at the start of the week, I felt like my students needed more support creating their models so I began the lesson going over what a model might look like for the plastic bottle magnet demo from the start of the week.
Ignore the end of the semester note the demo shared the board with, I don't have much white board space in my room.
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