How can you find the polarity of an electromagnet?

• A. Hold the electromagnet in your left hand with your fingers encircling the coil in the direction of current; the thumb points to the north pole.
• B. Hold the electromagnet in your left hand with your fingers encircling the coil in the direction electrons flow; your thumb will point to the north pole of the electromagnet.
• C. The north pole is determined by the direction of current entering the coil.
• D. Use a compass to locate the north pole.

Answer: (B)

Polarity is determined by the direction of current around the winding. The familiar hand rule says: curl your fingers in the direction of current around the coil and your thumb points to the north pole. If you think in terms of electron flow instead of conventional current, you can use the left hand with the fingers curling in the direction electrons move; your thumb will point to the north pole. This works because electron flow is opposite to conventional current, so using the opposite hand keeps the same mapping between the circulation direction and the pole.

The other ideas aren’t as reliable. Simply saying the north pole comes from the direction of current entering the coil doesn’t hold because the current travels around the entire loop, not just at a single entrance. And relying on a compass can be misleading in a setup with its own magnetic field and Earth's field, whereas the hand-rule method directly links circulation direction to pole orientation.