Science Buddies: "Ask an Expert"

I have copper wire, and iron nail and a volt-9 battery. I coiled the copper wire over 70 times around the iron nail and connected the wire to my battery. My battery became really hot. What did i do wrong! It wont lift the paperclips!

I suspect that the battery is getting hot because too much current is flowing through the magnet. A 9v. battery is intended to provide low current for a long time.
Are you following a recipe from the web? If yes, please let me have the url.
A 1.5v. D cell or a 6v. lantern battery can provide much larger currents than your 9v. You might try one of those.

You need to read up on ohms law. The resistance in your wire is too low. Based on what got hot, the internal resistance in the battery much higher than the resistance of your wire. You need to modify your circuit to limit the current flow. You could decrease the voltage (use a 1.5 V cell) and put an appropriate value resistor both in terms of ohms and watt dissapation capabilities in series.

The previous suggestion of a 6v lantern battery (lower voltage, a lot lower internal battery resistance, and a much bigger volume and surface area to disappate heat) would mean that it could supply more current for a longer period of time without getting as hot.

ComputerGeek - I agree with the previous comments. You should be using a fairly small gauge enameled copper wire. Perhaps 24 Ga or smaller (bigger number). The magnetic strength is determined by the amperage and number of turns of wire in the coil. A 1.5 V "D" battery cell should give you sufficient current to produce reasonable magnetic strength to easily pick up paper clips. Here are a couple of examples of what 70 turns of wire on a common large nail (say 1/4" diameter) would be for these smaller gauge wires and a "D" cell at 1.5V:

# 24 wire = about 50" of wire = about 1.25 ohms resistance = about 1.2 amps or 84 ampere turns

# 28 wire = about 50" of wire = about 4.55 ohms resistance = about 0.264 amps or 18 ampere turns

# 30 wire = about 50" of wire = about 7.21 ohms resistance = about 0.208 amps or 15 ampere turns

You can find the electrical specifications by looking up a copper wire table on the internet. My guess is that you were using a much larger wire gauge than was suitable for a 9V battery and effectively creating a short circuit, so little current flowed. Looking at these numbers, I would estimate that a 1.5V "D" cell would give you good results with # 28 or smaller diameter wire.

Good luck with your experiment.

Rick Marz

I have a 14.5in nail with a diameter of approximately half an inch, pretty big. I received my first source from this little kid believe it or not... -_-
URL: [http://www.youtube.com/watch?v=nMmldOU6t8l]
I believed his theory because all the videos and resources I took a looked at looked similar.
[http://www.ehow.com/video_4766167_creat ... agnet.html]
I believe from the recent videos i've seen my battery seems too weak for such a thick nail I have. I think it is a volt 9 battery but its not big, it's a small rectangle.
Maybe the copper wire i have as well because its solid and thin.
I greatly appreciate your support with my experience, I am currently on break until next tuesday and I would like to have this theory in my head to start because i believed this is due October 24th but all the other kids are getting a head start.

Rick can you please clarify? So a smaller, thinner wire and a weaker battery?
And Craig so you think a thinner wire as well?
Also my status hasn't been updated.

ComputerGeek - What is the diameter and insulation of the wire you are using. A nail, or spike, as large as you describe might be too large for the task of simply picking up paper clips. The "D" cell I mentioned is capable of several hundred milliamps of output for a reasonable period of time. With a 0.5" diameter spike, each turn on the coil is over 1.5" of wire, so 70 turns of copper wire is much higher resistance than the values I originally suggested. A smaller nail might be a good option. Give us some more information and I'm sure we can help.

Rick Marz

ComputerGeek wrote:I have a 14.5in nail with a diameter of approximately half an inch, pretty big.

Do you have a strong permanent magnet? If you do, then you could do a comparision of how many paperclips the permanent maget will pick up vs how many your nail with a permanent magnet on the head of your 14.5" nail will pick up. I expect the results to be enlightning. Just because something is large and massive and made from iron/steel doesn't make it a good candidate for an electromagnet core.

You need to do some reading on magnetic fields and magnetic core materials.

I believe at 150 copper coils i was picking up 15-18 paperclips for 400 coils should i be able to lift 45? Because at points it does not lift because I accidently overlap one time or the battery is not
functioning.

Putting more turns of wire on your nail will make the magnetic field in the nail stronger only up to a certain level. All materials have a "saturation field" that is the maximum magnetic field they can carry. Before you reach the saturation field, in general, more turns of wire will make a stronger field, but the field is not exactly proportional to the number of turns due to wire resistance, partial saturation, placement of the wire, and other factors.