All magnets have two poles - positive and negative. In order to make a negative charge magnet, you will have to make a simple magnet. A simple magnet is created by running an electrical current through a metallic object. The charge from the electrical source helps to create a charge on the metallic object which, in turn, will generate a magnetic field.
Strip both ends of the wire. Make sure there is about half an inch or so of bare wire exposed. The rest of the wire should remain shielded with the plastic sheathing.
Wrap the wire around the nail as tightly as you can. Start at the head of the nail, and work your way down to the tip. The tighter you wrap the wire, the stronger your magnetic field will be. Do not overlap the wire, but simply make as many single-file coils around the nail as you can. Leave roughly half a centimeter at the end of the nail tip.
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Wrap one of the bare ends of the wire around the positive terminal of the battery. Next, wrap the other bare wire around the negative terminal of the battery. You now have a functioning magnet.
Move the nail tip over a paperclip or metal filings to verify that the magnet is functioning properly. Repeat Steps 1-3 with another battery, some wire and a nail. With two magnets, you can now check to see that you have created a negative charge on your magnet.
You can use a Gaussmeter to verify which end of the nail carries a negative charge, however, these devices are extremely expensive. An inexpensive method to determine the positive and negative charge is by using a compass. Bring the compass near one end of the nail, and watch the needle. It will point towards "North" if it is positive, and "South" if it is negative.