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․ Temporary magnets are used in which of the following ?
All of these.

Permanent magnets lose their power after some days. So, if we use permanent magnet in those equipment, then it does not give efficient output throughout its entire life span. But, the above mentioned equipment have to work efficiently at all time. That is why the temporary magnets (or) the electromagnets are used in the above mentioned machines.

03․ Magnetic moment is a
pole strength.
universal constant.
scalar quantity.
vector quantity.

The magnetic moment can be considered to be a vector quantity with direction perpendicular to the current loop in the right hand rule direction. The amount of magnetic moment created by the current loop is μ = I × A. Where, I is current flowing through the loop and A is the area covered by the loop. So, the torque generated by the magnetic moment is T = μ × B. Where, B is the magnetic field. This torque tends to line up the magnetic moment with the magnetic field B, so this represents its lowest energy configuration. The potential energy associated with the magnetic moment is U (ø) = - μ × B. The cross sign represents that the magnetic moment is vector quantity.

04․ What is the dielectric constant of mica ?
3 to 8.
1 to 2.

The following are dielectric constant of different materials. They are, 1. Vacuum - 1 2. Glass - 5 to 10 3. Mica - 3 to 8 4. Mylar - 3.1 5. Neoprene - 6.70 6. Plexiglas - 3.40 7. Polyethylene - 2.25 8. Polyvinyl chloride - 3.18 9. Teflon - 2.1 10. Germanium - 16 11. Strontium titanate - 310 12. Water - 80.4 13. Glycerin - 42.5 .

05․ 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.

06․ 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.

07․ Why diamond is very hard ?
Because of large cohesive energy
Because of covalent solid
Because of high melting point
None of the above

Because it is composed of extremely small carbon atoms packed extremely tight, where they share atoms in a type of bonding known as covalent bonding as a cubic structure.

08․ 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.

09․ 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.

10․ When will be the electron pair bonding occurs ?
Lack holes
Share electrons
Share holes
None of the above

Covalent bonding occurs when pairs of electrons are shared by atoms. These electrons are shared in between them, so they stable by attraction forces between them.