MCQs on Engineering Materials

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01․ 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.

02․ Permanent magnets are used in
loud speakers.
all of above.

Temporary magnets are nothing but the electromagnets. Those magnets are used in lots of electrical appliance such as alternator, synchronous motors, etc. Because, for a large system, we could not create a permanent magnet and even if we create the permanent magnet, the life of that magnet is very less. That is why we usually use the electromagnet for that application.

03․ A degaussing is the process of
removing gases from materials.
removal of magnetic impurities.
demagnetising metallic parts.
remagnetising metallic parts.

Degaussing is the process of de-magnetizing or eliminating an unwanted magnetic field. Due to magnetic hysteresis, it is generally not possible to reduce a magnetic field completely to zero. But degaussing typically induces a very small known field to eliminate the unwanted magnetic field.

04․ Almost the entire mass of an atom is concentrated in the

Basically the nucleus is surrounded by electrons. The nucleus contains protons and neutrons, which are about 2000 times more massive than the electrons outside the nucleus. That is why most of the mass of the atoms are concentrated in nucleus.

05․ All ions of an element have the same
atomic number.
number of electrons.
number of protons.
both option A. and C.

Each of the ions of an element must have same number of protons. Actually, an ion may lose or gain the electrons further. Also atomic number of an element is defined by the number of protons present in the nucleus of that element.

06․ According to the Bohr model, an electron gains or losses energy only by
moving faster or slower in an allowed orbit.
jumping from one allowed orbit to another.
being completely removed from an atom.
jumping from one atom to another atom.

As per Bohr model, the electrons can only travel in special orbits at certain discrete set of distances from the nucleus. It is does not lose energy while they travel. They can only gain and lose energy by jumping from one allowed orbit to another.

07․ The number of rings in the Bohr model of any element is determined by what?
Column number on periodic table.
Atomic mass.
Row number on periodic table.
Atomic number.

Each electron shell can hold certain number of electrons. For example,
Electron Shell No of Electron
1 2
2 8
3 8
4 18
5 18
6 32
7 32
As per this table, there were seven electron shells which contain some number of electrons. The orbit is nothing but rings. The number of rings in the Bohr model of any element is determined by row number on periodic table.

08․ How many valence electrons would be found in an atom with the atomic number of 51?
none of above.

Antimony element has the atomic number of 51. The valence electrons are referred as the free electrons which are available at the last orbit. In antimony, the total electron shells are 5. They have the following number of electrons with them. First energy level : 2 Second energy level : 8 Third energy level : 18 Fourth energy level : 18 Fifth energy level : 5 Thus, the number of valance electron is 5.

09․ The Bohr model of the atom
explained the color lines in the hydrogen spectrum.
could not explain the line spectrum of atoms larger than hydrogen.
had some made-up rules without explanations.
all of the above.

The Bohr model is a relatively primitive model of the hydrogen atom, compared to the valence shell atom. As a theory, it can be derived as a first-order approximation of the hydrogen atom using the broader and much more accurate quantum mechanics.

10․ Maximum number of electrons in a sub-shell with l = 3 and n = 4 is

According to the Paulis exclusion principle, the maximum number of electrons in a given sub-shell is 2( 2×l + 1 ). Hence, 2( 2×l + 1 ) = 2( ( 2 × 3) + 1 ) = 14. So, the number of electrons in that sub-shell is 14.