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MCQs on Engineering Materials

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01․ ________ is the most detrimental impurity in the magnetic materials

All the four elements are used as impurity in magnetic material. They affects the regular geometric patterns and magnetic properties. Among these carbon is most detrimental or harmful. So, percentage of carbon is allowed up to 0.01.
02․ How many classes of insulating materials are there?

7 insulating material classes are : Y, A, E, B, F, H and C. They are classified depending upon the maximum limit of temperature withstand capacity. An easy way to remember this is: You Are Earning Bread For Her Comfort.
03․ What are insulating materials that can tolerate maximum temperature?
All of these.

Class C insulator consisting of mica, porcelain, glass and quartz with / without an inorganic binder can tolerate temperatures greater than 180o.
04․ What is the value of dielectric constant of air?
Less than 1
none of these.

Air has a dielectric constant or relative permittivity of 1, i.e. equal to the permittivity of vacuum.
05․ Which of the following is the example for piezo-electric material ?
Lead zirconate titanate
Potassium niobate
None of the above

Lead zirconate titanate,{Pb[ZrxTi1-x]O3 (0≤x≤1)}, an inter metallic, inorganic compound is the most common piezoelectric ceramic use today.
06․ What is the name of the fluorescent material that gives red colour fluorescence?
Zinc silicate.
Calcium silicate.
Zinc sulphide.
Magnesium silicate.

The magnesium silicate material gives red colour fluorescence. The cerussite (lead carbonate) gives bright green colour fluorescence. The zinc arsenate gives bright colour fluorescence.
07․ Which of the following is the least desired property in magnetic materials for electrical engineering applications ?
High magnetic permeability.
High electrical resistivity.
Large hysteresis loop.
All of the above.

High Permeability is desired because it helps in electromagnetic induction. High resistivity is required for good current conduction in conductor. But large hysteresis loop will increase hysteresis losses, so it is not desired. When a magnetic material is subjected to a cycle of magnetization (magnetized first in one direction and later demagnetized in opposite direction in a cyclic manner), energy loss takes place. This energy loss is due to molecular friction in the material. This energy loss is nothing but the hysteresis loss. So, for a large hysteresis loop, the point of hysteresis loss (or) magnetic saturation point is high. Hence, the effect of hysteresis loss is less in this case. That is why in the electrical applications, the magnetic material should not have larger value of hysteresis loop.
08․ The magnetisation and applied field in ferromagnetic materials are related
non linearly.

When a ferromagnetic material is magnetized in one direction, it will not come back to zero magnetization even the magnetizing field is removed. That is why the material follows a non-linear magnetization curve when the magnetization starts from zero field value.
09․ The materials which exhibit the same elastic properties in all directions are called
visco elastic.

Isotropy is uniformity in all orientations; it is derived from the Greek isos ( equal ) and tropos ( manner ).
10․ The dielectric strength of ferroelectric materials depends to a large extent on
area of hysteresis loop for the material.
presence of magnetic materials in the vicinity.
intensity of electric field.
frequency of applied voltage.

The dielectric strength of ferroelectric materials depends to a large extent on intensity of electric field applied.
11․ The potential gradient across the material of low permittivity is ______________ than across the material of high permittivity.
both (A) and (B).
none of above.

We know that the force development by a charged particle is F = Q / (4πεd2).The electric force F and electric field E are related as F = Q × E. Therefore, if we apply this relation with first expression, we would get E = 1 / (4πεd2). Hence, for low permittivity the potential gradient is greater than the high permittivity.
12․ Materials which lack permanent magnetic dipoles are called
none of the above.

Materials which lack permanent magnetic dipoles are called diamagnetic. Unlike a ferromagnet, a diamagnet is not a permanent magnet. Its magnetic permeability is less than μ0 (the permeability of free space).
13․ Which of the following is the ferroelectric material ?
Rochelle salt.
Potassium dihydrogen phosphate.
Barium titanate.
All of the above.

Ferroelectricity is a property of certain materials that have a spontaneous electric polarization that can be reversed by the application of an external electric field. The term is used in analogy to ferromagnetism. Ferromagnetism was already known when ferroelectricity was discovered in 1920 in Rochelle salt. Potassium dihydrogen phosphate and Barium titanate are also examples of ferroelectric materials.
14․ Materials having a high dielectric constant, which is non-linear, are known as
ferroelectric materials.
super die-electrics.
hard die-electrics.

Because of its property of electric polarization, high dielectric have non-linear electric field.
15․ In ferromagnetic materials
the atomic magnetic moments are antiparallel and unequal.
the atomic magnetic moments are parallel.
the constituent is only iron.
one of the constituent is iron.

In ferromagnetic materials the atomic magnetic moments are parallel and in the same direction.
16․ 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.
17․ 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.
18․ 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.
19․ 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.
20․ 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.

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