(a) An electromagnet consists of a core made of a ferromagnetic material placed inside a solenoid. It behaves like a strong magnet when the current flows through the solenoid and effectively loses its magnetism when the current is switched off.
(i) A permanent magnet is also made up of a ferromagnetic material but it retains its magnetism at room temperature for a long time after being magnetised once.
(b) (i) High permeability
(ii) Low retentivity
(iii) Low coercivity