(d) 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 not both are magnetised ? If only one is magnetised, how does one ascertain which one '? [Use nothing else but the bars A and B.]

Explanation

(d) Out of two iron bars, keep the tip of upper bar say first bar in contact with one end of second bar and then slide it along the length of second bar. If upper bar experiences strongest attractive forces while sliding near the ends of lower bar then lower bar is a bar magnet and upper bar is a simply an iron bar only, because magnetism of a bar magnet is present maximum at its two ends.