You are in a room with no metal objects except for two iron rods. Only one of them is a magnet. How can you identify which one is a magnet?
Answer
Solution 1: Hang the rods on a string and see which one turns to north.
Solution 2: Take one rod (A) and touch with its end the middle of the second rod (B). If they get closer, rod A is a magnet. This is because magnets will have magnetic field at the poles, but not in the center.