Magnets and Charge

Ask questions about projects relating to: aerodynamics or hydrodynamics, astronomy, chemistry, electricity, electronics, physics, or engineering.

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Magnets and Charge

Postby proudsnowmom » Sat Oct 06, 2012 7:15 pm

:? Why aren't my iron nails picking up my metal filings? I'm using a 9v battery with about a 4in iron nail, wrapped with insulated copper wire stripped the end but not picking up filings. Could it be because the copper wire is threaded type instead of single? Is battery not strong enough? Do I need larger nails? Thanks.
Posts: 1
Joined: Sat Oct 06, 2012 12:58 pm
Occupation: Student
Project Question: Doing Magnets and Charge, using a 9-volt battery and metal shavings from the auto parts store. Did everything as instructed but the nails are not picking up any metal. How "large" should the nails be and is a 9volt strong enough?
Project Due Date: 10/12/12
Project Status: I am conducting my experiment

Re: Magnets and Charge

Postby kgudger » Mon Oct 08, 2012 8:20 am

Hello and welcome to the forums:

Are you doing this project?
I think there might be some problems with this project, and I will ask the administrator about it.
In the meantime, do you have a way to measure the voltage of your battery? (A voltmeter?) If possible, please check the voltage of the battery when it's not connected and when connected to your coils, and report back to us the numbers you get.
If possible, it would be better to try this experiment instead, as it seems like it will work better:
Let us know what you decide.
Posts: 421
Joined: Wed Sep 17, 2008 9:20 pm
Occupation: electronic engineer
Project Question: n/a
Project Due Date: n/a
Project Status: Not applicable

Re: Magnets and Charge

Postby John Dreher » Mon Oct 08, 2012 2:04 pm

Kgudgers advice about projects makes a useful point. I have a speculation about what may have happened. A coil of wire has a very low resistance, thus by Ohm's Law, it will draw a very large current when placed directly across the terminals of a 9V battery. This very large current will, in turn, deplete the charge of the battery in a very short time. I would guess, then, that your battery is now dead. To prevent this from zapping your next battery you will need to put a resistor in series with the battery. A 100 ohm resistor will limit the current to (9 volts/100 ohms) = 0.09 amps. I think this is a plausible current (it depends on the number of turns of wire you used) to generate a magnetic field strong enough to attract iron filings while not discharging your battery too fast. Bear in mind that this is really a VERY crude guess on my part -- you may need to fiddle with the resistor to get enough magnetic field for your needs, or perhaps better, add more turns of wire if the magnetic field is a bit feeble. To check the battery you really need a voltmeter as kgudgers said. Here is a link to a cheap meter that would do the trick for under 10 dollars:

Best wishes for a magnetic tomorrow :)
John Dreher
Posts: 294
Joined: Sun Dec 25, 2011 8:33 am
Occupation: Astronomer, Professor of Physics, SETI Researcher (retired)
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Project Status: Not applicable

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