Two identical looking iron bars A and B are given, one of which is definitely known to be magnetised. (We do not know which one). How would one ascertain whether or noth both are magnetised ? If only one is magnetised how does one ascertain which one ? (Use nothing else but the bars A and B).

Explanation

Try to bring different ends of the bars closer. A repulsive force in some situation establishes that both are magnetised. If it is always attractive, then one of them is not magnetised. In a bar magnet the intensity of the magnetic field is the strongest at the two ends (poles) and weakest at the central region. This fact may be used to determine whether A or B is the magnet. In this case, to see which one of the two bars is magnet, pick up one, (say A) and lower one of its end first one of the two bars is magnet, pick up one, (say, A) and lower one of its end first one of the ends of the other (say, B) and then on the middle of B. If you notice that in the middle of B, A experiences no force, then B is magnetised. If you do not notice any change from the end of the middle of B, then A magnetised.