If you really want to understand electric circuit theory, eventually you will need to come to terms with Ohm’s Law. So how can you get the concept across that I=VR? Will your students be able to figure out that V=I/R or that R=V/I, or that all three of these equations are pretty much the same? How can they integrate these theories with their changing letter designations so they can be used in real life applications? How about throwing some throwies at them?

Many instructional materials for learning to work with electricity and circuits are based on 9 volt batteries. Often they start by having the experimenter place a resistor in series with the LED to reduce current flow, save on battery life and keep the LED from getting fried. Having to use a resistor at such an early stage of learning circuits introduces too much theory at the beginning. 9 volt batteries are also either moderately or unreasonably expensive.

There are many online resources for studying electricity and circuits. I particularly like one from Paul Falstad, which shows visuals for the current flow and direction. You can use his sample circuits, and modify them as well. He has many other visualizations of various math and physics concepts on his site.

Some of the ideas that you can pursue by using throwies are: How long will a throwie stay lit? If you add a second, third, or dozen LEDs in parallel to the 3volt battery, how will that affect the run time of the circuit? If you wire the same number of LEDs in series to the battery, how will that affect the duration of the life of the battery? If you add other components to the circuit, like, resistors, capacitors, transistors or photo resistors, how will the circuit behave? How do you use a multimeter to determine voltage, resistance, amperage, polarity and more?

Another reason to look to throwies is expense. If you take a look at the picture at the top of this post, from Make: Volume 6, page 116, you can find sources and prices for all the parts you need. LEDs are pretty cheap now. The batteries are reasonably priced as well, the magnets will cost some. You should be able to outfit a class full of throwie making supplies for relatively short money, but most of these parts can be harvested out of junk. LEDs are in most of the electronics that we throw out every day. Batteries are in every computer heading for the loading dock, and inside every hard drive is at least a couple of good high strength rare earth magnets. The older electronics are actually better for scavenging than a lot of the new stuff, since the parts were bigger and assembled with more traditional fasteners. If you are going to desolder components, you will need at least a soldering iron and some desoldering braid to go with your safety glasses.

One possible pitfall for this project is the magnets. They are definitely a source of potential mayhem in the hands of the average teenager. Certainly there are some ways to modify the project to minimize the chaos. Sittees? Stickies? Floaties?

Have you taught electricity with throwies or other simple materials? If you give it a try, take some pictures, video or make a posting to the Make Flickr Pool. Add some links to the descriptions. Add some comments to this post with more ideas on great ways to get students excited about learning electricity!

Are there other articles in Make or Craft that you think work well in the classroom or other learning environment? Post your ideas in the comments.

## 6 thoughts on “Make throwies to learn Ohm’s Law”

1. Jeff says:

I think you mean V=IR, not V=I/R

2. Chris Connors says:

Thanks Jeff. I fixed the error and added some more links to sites explaining the calculations. How do you use Ohm’s Law?

3. david says:

more ways to freak out boston!