Double-Coil Electromagnets?

[halkelley]

I'm doing a science fair project with my son that uses a "double-coil electromagnet".  Essentially you wind two coils around an iron core (iron bolt in this experiment) and then attach the pairs of leads to opposite ends of the battery.  This is supposed to make a stronger electomagnet.  Problem is I can't find anything on double-coil electromagnets anywhere.  I'm not sure if you are supposed to wind the coils on top of each other or on opposite ends of the bolt or some other option.  It also appears the directions are to attach both ends of coil A to one side of the battery, and both ends of coil B to the other side of the battery.  This would mean no current flows, as far as I can tell.  So I'm not confident I have good directions on how to hook up the four wires (two ends from each coil).  Any help would be appreciated. The experiment is described here:

http://books.google.com/books?id=NndskU55890C&pg=PA27&lpg=PA27&dq=double+coil+magnet+sci



ence+fair+project&source=bl&ots=tm9_rFbL2v&sig=SFGZBnN1gBNGAtAxIyM6VXDXNpQ&hl=en&



;ei=Z-0ASuDuN93flQectbzsBw&sa=X&oi=book_result&ct=result&resnum=1#PPA29,M1

[TheCasualTraveler]

     I could not make heads nor tails of that project. It says to use uninsulated wire which wrapped around a steel bolt will just be a dead short.

     Electromagnets are pretty simple. If you pick up a cheap $5 bag of magnet wire (wire with a clear coat of varnish type insulation)from Radio Shack all you need to do is wrap the wire around something steel like a bolt , bare the ends of the wire and hook it up to a battery (careful the battery is not too big or it will be more like a branding iron)Presto, electromagnet! If you can do that you can make up your own experiment.

     Must you use that particular experiment or will anything with electromagnets do? My first impression when I read that you need 4 oatmeal boxes was that it was sponsored by the good folks at Quaker Oats.

[willib]

Yeah i couldnt understand why they used uninsulated wire either..

On pg. 27 in the pdf they describe a single coil magnet, and a double coil magnet.

apparently its just two different coils wound around your bolt, hooked so that they will aid each other.

As most science books go these days, this one also leaves a lot to be desired.

[FuddyDuddy]

I did notice when you read the "experiment" before this one that they state

"uninsulated (enamealed) copper wire" .... But for this one they leave the

"(enamealed)" part off. Maybe just a typo ??