Quiz: Mechanical Engineering 2 June 2020

Quiz: Mechanical Engineering
Exam: ISRO
Topic: Material science

Each question carries 1 mark
Negative marking: 1/3 mark
Time: 10 Minutes
Q1. Atoms are arranged in face centred cubic (FCC) structure as
(a) All eight corners of the cube
(b) All eight corners of the cube and one of the body center
(c) All eight corners of the cube and at the center of each face
(d) All eight corners of the cube and one at the body center with one at the center of each face

Q2. Which of the following are zero dimensional defects?
1. Vacancy
2. Interstitial defect
3. Substitutional defect
(a) 1 and 2 only
(b) 1 and 3 only
(c) 2 and 3 only
(d) 1, 2 and 3

Q3. The number of electrons found in the outer most orbit of semi-conductor materials is,
(a) 2
(b) 4
(c) 6
(d) 8

Q4. What is the packing factor of FCC crystal structure?
(a) 0.64
(b) 0.68
(c) 0.74
(d) 0.78

Q5. Which is false statement about annealing?
(a) Annealing is done to relieve stresses
(b) Annealing is done to harden steel slightly
(c) Annealing is done to improve machine characteristics
(d) Annealing is done to soften material

Q6. Pearlite is a combination of:
(a) Ferrite and cementite
(b) Cementite and gamma iron
(c) Ferrite and austenite
(d) Ferrite and iron graphite

Q7. The Burger’s vector lies parallel to the dislocation line along the axis of a line of atoms in the same plane in:
(a) Screw dislocation
(b) Edge dislocation
(c) Cracks
(d) Vacancies

Q8. The atomic bond found in diamond is:
(a) Ionic
(b) Covalent
(c) Metallic bond
(d) None of these

Q9. Carbon content is highest in:
(a) Mild steel
(b) Eutectoid steels
(c) Hypoeutectoid steels
(d) Hypereutectoid steels

Q10. Which of the following is non-destructive test
(a) tensile test
(b) charpy test
(c) cupping test
(d) radiography test

S1. Ans(c)
Sol. Atoms are arranged in face centred cubic structure as all eight corners of the cube and at the centre of each face.

S2. Ans(d)
Sol. Defects in metal
(1) Point defect or zero dimensional defect
(a) Vacancy defect
(b) Interstitial defect
(c) Substitutional defect
(d) Frankle defect
(e) Schottky defect
(2) Surface defect
(a) Grain boundary defect
(b) Twin boundary defect
(c) Tilt boundary defect
(d) Staking faults
(3) Line defect
(a) Edge dislocation defect
(b) Screw dislocation defect

S3. Ans(b)
Sol. The number of electrons found in the outer most orbit of semi-conductor materials is 4.

S4. Ans(c)
Sol. Type of cell Packing factor
Simple cubic (SC) – 0.52
Hexagonal Close packed (HCP) – 0.74
Body centered cubic (BCC) – 0.68
Face-centered cubic (FCC) – 0.74

S5. Ans(b)
Sol. Annealing reduces the hardness of the steel completely and improve toughness, it is complete softening process and increase ductility.

S6. Ans(a)
Sol. Pearlite consists of 87% ferrite (layer are thick) and 13% cementite (thin layer) arranged alternatively in a lamelle formation.

S7. Ans(a)
Sol. Screw dislocation:- When a part of Crystal displaced angularly over the remaining about some edge, the dislocation is called screw dislocation.
(i) Burger’s vector is parallel to the screw dislocation line, whose direction is perpendicular.
(ii) Screw dislocation creates shear stress and strain in the crystal.

S8. Ans(b)
Sol. The atomic bond found is diamond is covalent bond.
Covalent Bond:- It is also called homopolar bond. This bond result by mutual sharing of valence electrons of identical atoms. The electronic structure of an atom is relatively stable it has eight electrons in its outer valence shell, which sometimes an atom acquires by shearing electrons with an adjacent similar atom. Diamond, methane chlorine are typical examples.

S9. Ans(d)
Sol. Carbon content is highest in hypereutectoid steels.

S10. Ans(d)
Sol. radiography test is the non-destructive test. In the radiography test there is no role of force so there is no deformation takes place within the testing material.
After the testing material is able to perform its functionality without any kind of destruction.

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