Posts Tagged ‘Electromagnet’
I found this on MAKE magazine’s site. If you don’t subscribe to this magazine, you need to check it out. I get so much stuff from it, I consider it a professional journal. The electronic edition gives you all the back issues, and every issue is packed with really cool things to build.
The speaker is so simple, and again, the students loved it. You use magnet wire, this time around 34 gauge, a couple of rare earth magnets, a styrofoam plate, some paper and glue. The magnets get glued to a wood or cardboard base. You make a coil of the wire that loosely fits over the magnets and glue it to the back of the plate (I used hot glue). The plate is held off the cardboard with a couple pieces of paper acting as a shock mount. You pass an audio signal through the coil. It generates a magnetic field and is attracted and repelled by the magnets, just like in a commercial speaker.
You can find the same design on this page, it might just be the same guy, I didn’t check.
When I made this the first time, I used 24 gauge wire. I would definitely go for something thinner, like 34 gauge. The wire is available from Radio Shack if you didn’t order it from your supply catalog. I believe the thinner wire will create a better sound.
I sacrificed an pair of dollar store headphones so that I could connect the speaker and I used an old transistor radio because I didn’t want to take a chance and damage a student’s iPod. Better safe than sorry.
Make sure to have the students put their hand on the working speaker. They can feel the vibrations that are creating the sound waves. After all, that was the point of the activity in the first place.
I do this more as an activity than anything else. I end up trying to cover electricity and magnetism in about two weeks, not anywhere near what is needed. I try to make the material relevant because it’s above most of the students in my conceptual physics classes. This is one of those activities where they amaze themselves.
I got the plans for an electric motor design from the book “Teaching Physics with Toys” by Taylor, Poth, & Portman. This book is really geared towards K-9, but I figure that if I find the activity cool, then why wouldn’t an 11th or 12th grader. I have the 1995 edition, they have a new edition that I haven’t seen. I don’t even know if this activity is in the new edition.
You can find similar activities on the web. (Build It: Electric Motor), but I like the design in the book better. Basically, you need a D cell, a doughnut magnet (available at Radio Shack), some bare heavy wire, like 14 or 16 gauge, some transformer or magnet wire (22-28 gauge), and a piece of sandpaper.
You take an arms length of the transformer wire, leave about 2 inches and wrap the rest around a dowel 5/8″ dowel or a white board marker, then leave another 2 inches at the other side.
As you may be able to see from the picture to the left, the leads are wrapped around the coil to tie it all together. It is important to try to balance the coil so that the leads are along the centerline of the loop. Next, sand the ends of the magnet wire so that the red coating is gone and you can see bare copper.
The magnet goes on top of the battery and will hold the top lead in place. You bring the negative voltage up with a bare copper wire, we use tape to hold the negative lead in place. Make a loop at the top of each with a pair of plyers. Try to make the loops on top at the same height so the motor doesn’t slide sideways.
To start the motor, just put it all together. You usually have to remove the positive lead to fit the winding coil into the loops. Put the leads back on and pop the magnet in place. If its really well made, the motor will begin spinning on its own. That rarely happens. Just give it a light spin. You will need to play with the leads to get them centered, but then when you get it right, it can run for hours.