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Hard magnetic materials like tungsten-steel alloy or chromium-steel alloy are used in the manufacture of:
1. dynamo core
2. transformer core
3. permanent magnets
4. electromagnets
5. both (1) and (2)

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Correct Answer - Option 3 : permanent magnets
  • Generally, ferromagnetic materials are used for making permanent magnets. These materials include tungsten-steel alloy or chromium-steel alloy iron, nickel, cobalt, and some rare earth metals.
  • Steel is an alloy of iron and so can also be made into a permanent magnet. Alloys with less iron, nickel, or cobalt will be magnetically soft and have a weaker magnetic field.
  • Alnico (made of Aluminium, Nickel, and Cobalt) is also used for making a permanent magnet.

High-Frequency transformer Core:

  • Ferrites materials have a tendency to hold the magnetic flux within their core.
  • Ferrite is a ceramic compound consist of Iron oxide mixed with zinc, nickel and manganese compounds.
  • The ferrite core offers high resistance (or low electrical conductivity) which decreases the magnitude of eddy current, so losses reduce.
  • The ferrite core reduces magnetostriction noises.

 

Permanent Magnets:

  • Permanent magnets are magnets that retain their magnetism over long periods of time. Permanent magnets are made of hard ferromagnetic materials.
  • In a paramagnetic material, every individual atom (or ions or molecules) possesses a dipole moment.
  • And this magnetic moment of every atom interacts with one another in such a way that they spontaneously align themselves in a common direction over a macroscopic volume which is termed as the domain.
  • The magnetic strength of a magnetic material is inversely proportional to temperature, since as temperature increases because of thermal agitation orientation of atoms becomes random when leading to a decrease in its magnetic field, and after certain temperature magnetic material loses its magnetic property permanently.
  • Also, Temporary magnets are those which act like a permanent magnet when they are within a strong magnetic field but lose their magnetism when the magnetic field disappears. E.g. Electromagnet.

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