Explain why iron filings which are sprinkled on a sheet of cardboard placed over a bar magnet, take up a definite pattern when cardboard is slightly tapped.

The diagram below shows a current carrying loop or a circular coil passing through a sheet of cardboard at the points M and N. The sheet of cardboard is sprinkled uniformly with iron filings. Draw the pattern of arrangement of the iron filings when current is passed through the loop.

The diagram below shows a current carrying loop or a circular coil passing through a sheet of cardboard at the points M and N. The sheet of cardboard is sprinkled uniformly with iron filings. Copy the diagram and draw an arrow on the circular coil to show the direction of current flowing through it.

Sometimes when a vehicle is driven at a particular speed, a rattling sound is heard. Explain briefly, why does this happen and give the name of the phenomenon taking place. Suggest one way by which the rattling sound could be stopped.

(a) What happens if a bar magnet is cut into two pieces (i) transverse to its length (ii) along its length? (b) What happens if an iron bar magnet is melted? Does it retain its magnetism? (c) A magnetised needle in a uniform magnetic field experiences a torque but no net force. However, an iron nail near a bar magnet experiences a force of attration in addition to a torque, explain. (d) Must every magnetic field configuration have a north pole and a south pole? What about the field due to a toroid? (e) Can you think of magnetic field configuration with three poles? (f) Two identical looking iron bars A and B are given, one of which is definitely known to be magnetised. 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.