Question

Name the material of core in electric bell, electromagnet, d.c. motor, a.c. generator and transformer.

• A. soft iron
• B. hard iron
• C. soft steel
• D. hard steel

Answer 1

The correct option is A soft iron

A magnetic core is a piece of magnetic material with a high permeability used to confine and guide magnetic fields in electrical, electro-mechanical and magnetic devices such as electromagnets, transformers, electric motors, generators, inductors, magnetic recording heads, and magnetic assemblies. It is made of ferromagnetic metal such as iron, or ferrimagnetic compounds such as ferrites.
The magnetic field is often created by a coil of wire around the core that carries a current. The presence of the core can increase the magnetic field of a coil by a factor of several thousand over what it would be without the core. The use of a magnetic core can enormously concentrate the strength and increase the effect of magnetic fields produced by electric currents and permanent magnets.
The properties of a device will depend on the following factors:

• The geometry of the magnetic core.
• The amount of air gap in the magnetic circuit.
• The properties of the core material like permeability and hysteresis.
• The operating temperature of the core.
• Whether the core is laminated to reduce eddy currents.