Question

what is a magnet and how it is dismagnetise​

Answer 1

A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, and attracts or repels other magnets. 

Demagnetize a Magnet 

by Heating or Hammering. If you heat a magnet past the temperature called the Curie point, the energy will free the magnetic dipoles from their ordered orientation. ... You can get the same effect by repeatedly hammering a magnet, applying pressure, or dropping it on a hard surface.

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