MCQs on Engineering Materials

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01․ When a ferromagnetic substance is magnetized small changes in dimensions occur. Such a phenomenon is known as
magnetic hysteresis.
magnetic expansion.

Magnetostriction is a property of ferromagnetic materials that causes them to change their shape or dimensions during the process of magnetization.

02․ Magnetic recording tape is most commonly made from
small particles of iron.

Magnetic tape is a medium for magnetic recording, made of a thin magnetizable coating on a long, narrow strip of plastic film. Magnetic recording tape is most commonly made from silicon - iron .

03․ The permeability of iron can be increased by
purifying it.
alloying with cobalt.
reducing carbon percentage.
increasing carbon percentage.

The permeability of iron can be increased by alloying with cobalt.

04․ A material with unequal anti-parallel atomic magnetic moments is
an anti-ferromagnet.
a ferrite.

An anti-ferromagnet is a material with equal anti-parallel atomic magnetic moments. Ferrimagnet is like anti-ferromagnet but with unequal anti-parallel atomic magnetic moments. The oldest known magnetic substance, magnetite (iron(II,III) oxide); is a ferrimagnet.

05․ The temperature beyond which substances lose their ferroelectric properties, is known as
curie temperature.
critical temperature.
inversion temperature.
conversion temperature.

Materials are only ferromagnetic below their corresponding curie temperatures. Ferromagnetic materials are magnetic in the absence of an applied magnetic field. Curie temperature or curie point, is the temperature where a materials permanent magnetism changes to induced magnetism or vice versa.

06․ Positive magnetostriction exists when
dipoles are repel other.
dipoles are attract each other.
both are correct.
none of above.

During magnetization process of magnet the dipoles are attract and repel each other. Positive magnetostriction exists when dipoles are repel each other.

07․ The permanent magnets are made from which of following materials ?
Soft iron.

The ferromagnetic materials have high retentivity and lower coercivity. It helps to a permanent magnet that retains its magnetic properties for a long time even if we remove the applied magnetic field and magnetic materials from which permanent magnets are made, basically called as hard magnetic materials. Hence, the ferromagnetic materials are used to make permanent magnets.

08․ Indicate which of following material does not retain magnetism permanently
soft iron.
stainless steel.
hardness steel.
none of above.

This ability of a material to retain its magnetism is called Retentivity. Materials which are required to retain their magnetism will have a fairly high retentivity. But, soft iron has no retentivity. Hence, it does not retain magnetism permanently.

09․ Which statement is not true of ferromagnetic materials.
Energy loss is proportional to the area of hysteresis loop.
They have fixed value of μr.
They have large magnetic susceptibility.
They lose their nonlinearly property above the Curie temperature.

H curve is not linear. So μr is not constant.

10․ Which of following material has least value of dielectric constant?

The dielectric constant is the ratio of the permittivity of a substance to the permittivity of free space. The permittivity value of oil is less than the other above mentioned materials. Hence, the dielectric constant is less for oil.