Science Buddies: "Ask an Expert"

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.

Hello and welcome to the forums:

Are you doing this project? https://www.sciencebuddies.org/science- ... ml#summary
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: https://www.sciencebuddies.org/science- ... ml#summary
Let us know what you decide.
Keith

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:

http://tinyurl.com/8pwrz34

Best wishes for a magnetic tomorrow