Final answer:
A magnet made from iron exhibits magnetic properties because the magnetic domains within the material are aligned, allowing it to display a net magnetic field. An ordinary iron bar does not show a net magnetic effect because its domains are randomly oriented and cancel each other out.
Step-by-step explanation:
The reason a magnet made from iron has magnetic properties while an ordinary iron bar does not can be explained by the alignment of magnetic domains within the materials. Iron, nickel, and cobalt are ferromagnetic materials, meaning they can become magnetized. In an unmagnetized iron bar, the magnetic domains are randomly oriented and cancel each other out, so the bar does not display any net magnetic effect. However, when a material like iron is made into a magnet, the domains are aligned in the same direction, which causes the material to exhibit magnetic properties such as attraction to other metals and alignment with magnetic fields. Diamagnetism is a property of materials like copper or bismuth that become magnetized with a polarity opposite to the external magnetic field and are slightly repelled by a magnet, unlike iron which is strongly attracted. Ferromagnetic materials not only respond strongly to magnets but can also retain magnetization, becoming permanent magnets. This is due to the atomic-level currents within the domains that act as tiny magnets which align collectively in the presence of a magnetizing force.