The permanent magnets are those which retain their magnetism for a long time.
Which material is used for a permanent magnet?
The material which have gradually rising magnetisation curve, large hysteresis loop area and consequently large energy loss for each cycle of magnetisation are used for making permanent magnet, viz. Carbon steel, Alnico and hand ferrities etc. Generally carbon steel (Ni + CO) is used for making permanent magnets.
How a horse shoe magnet which has lost most of its magnetism will be magnetised?
The horse shoe magnet can be brought back in magnetised state by using an electromagnet method. Wrap the super enamelled wire over the magnet as shown in Fig. 11.12 and connect to d.c. low voltage supply, for sufficient time and intermittently. In this case the direction of current should be strictly observed. It can otherwise be magnetised on the pole charger the polarities must be observed carefully.
