try experiment with induction

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Home : 2005 : February : 21

try experiment with induction
By Chris

This is way late. I'm sorry I didn't see your message earlier. I'm not a teacher, but I have done lectures and demonstrations for classes before with electricity. I'm in college, and experimenting with electricity is one
of my hobbies. My mom's a teacher and I've done demonstrations for her class and others. There are a lot of things you can do. One of my favorite, and one that wouldn't be too hard to set up is a demonstration of induction. Wind two coils with 28 or 30 gauge magnet wire. A low voltage battery (from a flashlight will do) is connected to one coil. Connect a 9 volt battery to the other

coil, except with a switch to break the circuit. Put both coils around a magnetic "core" - a large nail or even a bolt will work. You will notice that each time you connect and disconnect the battery from the coil, the light bulb will light. But of course, it isn't continuous because the magnetic field has to be moving, so you have to have a pulsating current. The bulb will flash each time the battery is connected and disconnected. You will get varying results, depending on how many turns you have on the coils, the gauge of the wire, and the distance between the coils. You will have to play around with it a little to get the bulb to light. This demonstrates electromagnetic induction, and the principles at work in a transformer. The coils in this little experiment are like the primary and secondary windings in a transformer. You're basically making two electromagnets on the same core, with only one having power.

You can save a little bit of work, if you have an electronics store nearby. Look for a "solenoid coil," preferably one wound for AC. A solenoid is basically just an electromagnet. A lot of common items have solenoids...automatic sprinkler valves have solonoid coils to open and close the valve. For safety, you'll want one for low voltage, maybe 6 or 12 volts AC. If you find a solenoid, you can use that as a primary winding and then you just need to make a secondary. If you do use an AC solenoid, you will need a transformer to step the outlet line voltage down, but you can get one very easily and cheaply. A small 6 volt transformer at Radio Shack was about $5 the last time I saw. The kids can even try winding different size secondary coils on the "homemade transformer" and see how it effects the experiment. You can get a cheap analog multimeter ($10 or even less sometimes) and actually measure how the voltage on the secondary is affected by the size of the coil and number of turns. And of course, a multimeter will come in very handy for many other experiments.

There are so many things they could learn from this experiment...

1. Induction - two coils not connected. One is supplied with a pulsating current, and electricity is transferred to the other coil, which is shown by a bulb lighting each time the current is applied and disconnected momentarily.

2. Transformer action - Voltage (and current) can be varied by changing the number of turns on the secondary winding.

3. Frequency - the kids might catch on and understand what alternating current from an outlet (or the "AC mains" as we call it) really is. When we plug a lamp into an outlet, it is actually flashing just like the bulb was in the experiment, but it's flashing so fast that our eyes don't percieve it, so the light seems continuous. They may learn a new term, "frequency," meaning how fast an electric current is pulsating (or in the case of AC, how fast it is changing direction). Common household AC is 60 Hertz, or 60 cycles-per-second.

Electricity can definitely be a very fascinating subject to learn about, and I think 6th graders would be able to understand it. Of course, this experiment is really simplifying things...there are a LOT of other factors that go into a transformer, like things called "impedance," "inductive reactance," "current regulation"...but I definitely won't get into all that here!
:-)

If you can talk to someone who has a Tesla Coil, then you'd really be in business. You can find out more about a Tesla Coil online, but they generate very high voltage at radio frequency and can light up florescent and neon tubes without any wires! I built one a few years ago. A Tesla Coil generates some amazing effects, but they can be dangerous and have to operated by someone knowledgable.

I hope this helps some. Good luck. Try looking on Google for "induction" and "experiments," "school project," etc.

- Chris