You are taken to a dark room and given two thin long rods - 30 cm long and 1 cm thick. One of them is a permanent magnet and the other is pure iron which is not magnetized.
Both of them are insulated with glass. They weigh the same. The shapes are same too. How can you tell which one of these rods is the magnet? Remember, you can't see anything, and you cannot use anything other than these two rods in your investigation. You are not allowed to break them or remove the insulation either.