40872180 Material Science Objective Questions

MATERIAL SCIENCE & ENGINEERING AMIE

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AMIE(I) STUDY CIRCLE(REGD.) A Focused Approach

Objective Questions IMPORTANT NOTE

• Please read this chapter after going through all the theory chapters provided in this course.

• This chapters also includes questions asked in previous years.

• All the questions are not classified topic wise. Instead these are randomly selected to match examination conditions.

Set 1: Crystal Structure 1. Repeatable entity of a crystal structure is known as

a) Crystal

b) Lattice

c) Unit cell

d) Miller indices

2. Coordination number for closest packed crystal structure

a) 16

b) 12

c) 8

d) 4

3. Atomic packing factor is

a) Distance between two adjacent atoms

b) Projected area fraction of atoms on a plane

c) Volume fraction of atoms in cell

d) None

4. Coordination number in simple cubic crystal structure

a) 1

b) 6

c) 3

OBJECTIVE QUESTIONS (MAT SC.)

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d) 4

5. The atomic diameter of an BCC crystal (if a is lattice parameter) is

a) a

b) a/2

c) a/(4/√3)

d) a/(4/√2)

6. A family of directions is represented by

a) (hkl)

b) <uvw>

c) {hkl}

d) [uvw]

7. Miller indices for Octahedral plane in cubic crystal

a) (100)

b) (110)

c) (111)

d) None

8. The plane (111) is parallel to

a) ( 111 )

b) ( 1 11)

c) (111)

d) (111)

9. The angle between [111] and [112 ] directions in a cubic crystal is (in degrees)

a) 0

b) 45

c) 90

d) 180

10. Miller indices of the line of intersection of ( 1 11) and (110) are

a) [110]

b) [101]




c) [101 ]

d) [ 110 ]

11. The minimum number of ions in the unit cell of an ionic crystal with FCC space lattice is

a) 4

b) 8

c) 12

d) 16

12. If the radius of an atom in a simple cubic crystal is r, the body diagonal of the unit cell is

a) r√3

b) 2r√3

c) 4r/√3

d) 3r/4

----------Key to Set 1----------

1. (c)

2. (b)

3. (c)

4. (b)

5. (c)

6. (b)

7. (c)

8. (a)

9. (c)

10. (d)

11. (b)

12. (b)

Set 2: Defects in Solids 1. This figure shows the formation of

a) Schottky defect

b) Frankel defect

c) line defect




d) point defect

2. The Burgers vector of an edge dislocation is perpendicular to the dislocation

a) True

b) False

3. The energy of an edge dislocation is greater than that of a screw dislocation in the same material.

a) True

b) False

4. The imperfection in the crystal structure of metal is called

a) dislocation

b) cleavage

c) fracture

d) slip

5. Schottky defect is

a) a vacancy interstitial combination

b) a pair of oppositely charged ion vacancies

c) purely an interstitial defect

6. A dislocation in a metal represents

a) Weakness of the metal

b) Point defect in the metal

c) Volume defect in the metal

d) Line defect in the metal

7. Following is not the 2-dimensional imperfection

a) Twin boundary

b) Dislocation

c) Surface

d) Grain boundary

8. Figure out the odd one in the following

a) Frenkel defect

b) Tilt boundary




c) Twist boundary

d) Stacking fault

9. Thermodynamically stable defects

a) Point defects

b) Line defects

c) Surface defects

d) Volume defects

10. Conservative movement of dislocations

a) Slip

b) Climb

c) Both slip and climb

d) None

11. Burger’s vector changes with

a) Kind of dislocation

b) Length of dislocation

c) Both kind and length of dislocation

d) None

12. Which of the following is false?

a) Line defects are thermodynamically stable

b) Dislocation can end inside a crystal without forming loop

c) ABC ABC ABC…is stacking sequence for HCP crystal

d) All

13. Requirement for cross-slip movement of dislocation

a) Preferred slip plane

b) Preferred slip direction

c) No preferred slip plane

d) No preferred slip direction

14. Sharp break in dislocation line that is in slip plane _______________.

a) Jog




b) Kink

c) Either jog or kink

d) None

15. Minimum number of slip systems that must be operative during plastic deformation

a) 3

b) 4

c) 5

d) 6

----------Key to Set 2----------

1. (a)

2. (a)

3. (b)

4. (a)

5. (c)

6. (d)

7. (b)

8. (a)

9. (a)

10. (a)

11. (d)

12. (d)

13. (c)

14. (b)

15. (c)

Set 3: Diffusion In Solids 1. Diffusion can occur in ________________ materials.

a) Solid

b) Liquid

c) Gaseous

d) All

2. The units for diffusivity, D, are

a) m²sec

b) m²/sec

c) 1/m²sec

d) sec/m²

3. The following mechanism contributes very little the diffusivity




a) Vacancy

b) Interstitial

c) Substitutional

d) Self-interstitial

4. Example for steady-state diffusion

a) Hydrogen purification by palladium sheet

b) Doping semi-conductors

c) Corrosion resistance of duralumin

d) Decarburization of steel

. The most influencing factor of diffusivity

a) Diffusing species

b) Temperature

c) Lattice structure

d) Presence of defects

6. The following phenomena are useful in zone-refining process

a) Coring

b) Segregation

c) Both

d) None

7. For the same diffusion time, the depth of diffusion penetration at 500 and 850 degree Celsius is in the ratio of 1:6. The activation energy for diffusion is

a) 57 kJ/mol

b) 37 kJ/mol

c) 114 kJ/mol

d) 74 kJ/mol

8. If D₀ = 0.00004 m²/sec and Q = 100 kJ/mol, to double the depth of penetration, the initial temperature

of 900 degree centigrade should be increased to

a) 910⁰C




b) 923⁰C

c) 986⁰C

d) 1083⁰C

9. In a steel, during carburization at 937⁰C, 0.6% carbon is found at a depth of 0.2 mm after 1 hr. The

time required to get 0.6% C at double this depth at the same temperature is

a) 60 s

b) 1.414 hr

c) 2 hr

d) 4 hr

---------- Key to Set 3 ----------

1. (d)

2. (b)

3. (d)

4. (a)

5. (b)

6. (c)

7. (d)

8. (d)

9. (d)

Set 4: Phase Transformation 1. A martensitic transformation

a) consists of two stages, namely a nucleation stage and a growth stage

b) is extremely rapid

c) can only lead to a change in the crystal structure of the phases

d) can lead to a change in composition of the phases

e) does not involve diffusion

2. The eutectoid mixture of steel is

a) a mixture of ferrite and cementite

b) a mixture of ferrite and austenite

c) a mixture of austenite and cementite

d) called pearlite




3. Which of the following constituents of steel is softest and least strong

a) austenite

b) pearlite

c) ferrite

d) cementite

4. Hardness of steel depends on

a) amount of carbon it contains

b) the shape and distribution of the carbides in iron

5. Maximum percentage of carbon in ferrite is

a) 0.025 %

b) 0.8 %

c) 0.25 %

6. Eutectoid steel contains following percentage of carbon

a) 0.025 %

b) 0.8 %

c) 0.25 %

7. Hypo eutectoid steels have carbon content

a) equal to 0.83 %

b) less than 0.83 %

c) greater than 0.83 %

8. Hypo eutectoid steels have structure of

a) pearlite alone

b) Phases of ferrite and pearlite

9. Hypereutectoid steels have structure of

a) pearlite alone

b) phases of cementite and pearlite

10. The temperature at which new grains are formed in a metal is called

a) recrystallisation temperature




b) lower critical temperature

c) upper critical temperature

11. The temperature and carbon content at which eutectoid reaction occurs in Fe C equilibrium diagram are

a) 723º C and 0.02 % C

b) 723º C and 0.08 % C

12. Martensite is the supersaturated solution of carbon in iron.

a) true

b) false

13. Martensite are always hard.

a) true

b) false

14. Shifting of CCT curve to the _______ direction increases the hardenability of a steel.

a) left

b) right

15. During pearlite transformations

a) new phases form

b) crystal structure change

c) composition of phases changes

d) there is no diffusion

16. The hardness of martensite in an steel is a function of

a) C content

b) cooling rate

c) Ni content

d) nose location

17. Martensite transformations

a) are diffusion controlled

b) are shear processes

c) yield two products of different compositions




d) yield a hard product in steels

18. Bainite has

a) the same morphology as austenite

b) a non lamellar morphology of ferrite and cementite

c) the coarsest morphology among all the products from austenite

d) none of these

19. The free energy decrease during recrystallization comes mainly from

a) excess point defects

b) excess dislocations

c) grain boundaries

d) lower energy of the new crystal

20. The recrystallisation rate increases with

a) increasing amount of cold work

b) higher working temperature

c) higher annealing temperature

d) decreasing initial grain size

21. In a single component system, the maximum number of phases that can coexist in equilibrium is

a) 2

b) 3

c) 4

d) 5

22. The degree of freedom when ice, water and water vapour co-exist in equilibrium is

a) 1

b) triple pt

c) 0

d) -1

23. The degrees of freedom, when FCC iron and BCC iron co-exist in equilibrium, are

a) 2

b) 1




c) 0

d) -1

24. The phase boundary between alpha and (alpha + beta) regions is called

a) liquidus

b) solidus

c) solvus

d) none of these

25. The reaction that yields two solid phases on cooling a single solid phase is called

a) eutectoid

b) peritectoid

c) eutectic

d) congruent

26. If one solid phase splits into two solid phases on heating, the reaction is

a) eutectoid

b) peritectic

c) eutectoid

d) peritectoid

27. The reaction that, on heating one solid phase, yields another solid phase plus one liquid phase is called

a) eutectic

b) eutectoid

c) peritectic

d) peritectoid

28. If alpha of 82% B and liquid of 57% B are in equilibrium in an alloy of 73% B, the fraction of liquid is

a) 0.36

b) 0.64

c) 36%B

d) 0




29. If fraction of liquid with 57% B, which is in equilibrium with solid of 82% B, is 0.7, the overall composition is

a) 0.3

b) 74.5% B

c) 64.5% B

d) 25% B

30. The fraction of pearlite in a 0.55% C steel is

a) 0.55

b) 0.31

c) 0.69

d) 0

---------- Key to Set 4 ----------

1. (b) (c) (e)

2. (a)

3. (c)

4. (b)

5. (a)

6. (b)

7. (b)

8. (b)

9. (b)

10. (a)

11. (b)

12. (a)

13. (a)

14. (b)

15. (a) (b) (c)

16. (a)

17. (b) (d)

18. (b)

19. (b)

20. (a) (c) (d)

21. (b)

22. (c)

23. (b)

24. (c)

25. (a)

26. (d)

27. (c)

28. (a)

29. (c)

30. (c)

Set 5: Mechanical Properties 1. In primary creep the work hardening occurs mine rapidly than any concomitant recovery process

a) true

b) false




2. In secondary creep the

(select two options)

a) recovery rate is greater than the work hardening rate

b) recovery rate is equal to the work hardening rate

c) creep strain ε is given by ε = Kt, where K is constant and t is the time

d) creep strain is given by ε = Kt1/3

e) creep rate is independent of temperature

3. Slow plastic deformation of metal under a constant stress is known as

a) Creep

b) fatigue

c) endurance

d) non plastic deformation

4. The following types of materials are usually the most ductile

a) face centered cubic lattice

b) body centered cubic lattice

c) hexagonal close packed lattice

5. The relationship between hardness and % carbon for steel can be expressed by the curve

a) A

b) B

c) C

d) D

6. The relationship between tensile strength and % carbon for steel can be expresses by the curve




a) A

b) B

c) C

d) D

7. On Rockwell’s scale (scale for hardness), one Rockwell number is represented by penetration depth of

a) 0.0080 inch

b) 0.00080 inch

c) 0.000080 inch

d) none of the above

8. Ductility is measured in terms of

a) Ultimate tensile strength

b) Percentage elongation

c) Modulus of toughness

d) Modulus of resilience

9. Proof stress corresponds to

a) Lower yield point

b) Higher yield point

c) Elastic limit

d) a specific strain

10. Which hardness method can be used to measure hardness of a single grain ?

a) Rockwell

b) Knoop

c) Vickers

d) Shore




11. Creep of solid occurs at

a) half the melting point or above on absolute scale

b) temperature above 4000 C

c) any temperature

12. As compared to engineering stress strain curve, the true stress strain curve is

a) above and to the left

b) below and to the right

c) crosses the engineering curve

d) parallel to the engineering curve

13. In a tensile test, the engineering stress corresponding to the maximum load is called

a) yield strength

b) tensile strength

c) UTS

d) upper yield stress

14. In a tensile test, necking starts at

a) lower yield stress

b) upper yield stress

c) ultimate tensile stress

d) just before fracture

15. In the Griffith equation, the fracture stress is proportional to

a) √c

b) 1/√c

c) 1/c

d) 1/2c

16. If the surface crack causing fracture in a brittle material is made twice as deep, the fracture strength will

a) decrease by a factor of √2

b) decrease by a factor of 2

c) decrease by a factor of 4




d) not change

17. The fatigue strength of mild steel is

a) equal to its tensile strength

b) more than its tensile strength

c) equal to its yield strength

d) lower than its yield strength

---------- Key to Set 5 ----------

1. (a)

2. (b) (c)

3. (a)

4. (a)

5. (a)

6. (b)

7. (c)

8. (b)

9. (c)

10. (c)

11. (b)

12. (a)

13. (c)

14. (c)

15. (b)

16. (a)

17. (d)

Set 6: Deformation of Metals 1. The combination of spring and dash pot in series is known as the Maxwell model

a) true

b) false

2. The elastic stress strain behaviour of rubber is

a) linear

b) non linear

3. The unique property of cast iron is

a) malleability

b) ductility

c) hardness

d) damping characteristics

4. Mechanical deformation of lead at room temperature is a __________ operation.




a) cold working

b) hot working

5. The Voigt-Kelvin element is a

a) series combination of an spring and a dashpot

b) parallel combination of an spring and a dashpot

c) four parameter model

d) none of these

6. A linear combination of a Maxwell and Voigt Kelvin element is a

a) one parameter model

b) two parameter model

c) three parameter model

d) four parameter model

---------- Key to Set 6 ----------

1. (a)

2. (a)

3. (d)

4. (b)

5. (b)

6. (d)

Set 7: Heat Treatment of Metals 1. Work hardening is a useful strengthening mechanism but it has the following disadvantages:

(Select two options)

a) only useful for two phase materials

b) decreases the ductility of the material

c) not suitable if the material is to be used at an elevated temperature

d) only applicable to single crystals

2. The presence of a dispersion of small particles increases the strength of a material by an amount that depends on the

(Select two options)

a) volume fraction of the particles

b) valency of the solute atoms




c) the size of the particles

d) the viscoelastic deformation rate of the particles

3. A martensitic transformation

(Select three options)

a) consists of two stages, namely a nucleation stage and a growth stage

b) is extremely rapid

c) can only lead to a change in the crystal structure of the phases

d) can lead to a change in composition of the phases

e) does not involve diffusion

4. Hardness of steel depends on

a) amount of carbon it contains

b) the shape and distribution of the carbides in iron

5. Cyaniding is the process of

a) dipping steel in cyanide bath

b) adding carbon and nitrogen by heat treatment of steel to increase surface hardness.

6. Process of Austempering results in

a) formation of bainite structure

b) formation of carburised structure

c) formation of martensitic structure

7. Materials after cold working are subjected to following process to relieve stresses

a) hot working

b) tempering

c) annealing

8. Annealing is done to harden steel

a) true

b) false

9. Heat treatment operation involving heating of steel above upper critical temperature and then cooling in the air is known as annealing .

a) true




b) false

10. Martensite is the supersaturated solution of carbon in iron.

a) true

b) false

11. The higher the temperature of tempering

a) the softer will be the product

b) the tougher will be the product

c) the harder will be the product

d) the stronger will be the product

12. Mechanical deformation of lead at room temperature is a __________ operation.

a) hot working

b) cold working

13. Martensite are always hard.

a) true

b) false

14. Fine grains are obtained by

(select three options)

a) slow cooling

b) increasing nucleon rate

c) decreasing growth rate

d) fast cooling

15. The c/a ratio of martensite depends on the concentration of

a) Ni

b) Mn

c) C

d) N

16. During overaging, hardness

a) decreases

b) increases




c) is constant

d) increase abruptly

17. Overageing refers to

a) ageing above room temperature

b) ultra fine precipitate size

c) long ageing

d) coarsening of precipitate particles

18. The most desirable method of increasing the yield strength of mild steel is

a) grain refinement

b) cold working

c) solute additions

d) precipitation hardening

---------- Key to Set 7 ----------

1. (b) (c)

2. (a) (c)

3. (b) (c) (e)

4. (b)

5. (b)

6. (a)

7. (c)

8. (b)

9. (b)

10. (a)

11. (a)

12. (a)

13. (a)

14. (b) (c) (d)

15. (c)

16. (a)

17. (d)

18. (a)

Set 8: Engineering Materials 1. A cast iron


a) is re-melted and cast pig iron

b) is the product of the blast furnace

c) has a carbon content in the range 0.2 to 0.2 wt % C

d) has a carbon content in the range 0.2 to 0.5 wt % C




e) always contains pearlite

f) always contains martensite

2. The viscosity of glass decreases linearly with increasing temperature

a) true

b) false

3. Concrete goes on hardening for years

a) true

b) false

4. Mild steel belongs to the following category

a) low carbon steel

b) medium carbon steel

c) high carbon steel

d) alloy steel

5. The elastic stress strain behaviour of rubber is

a) linear

b) non linear

6. Isotropic material are those which have the same

a) elastic properties in all directions

b) stresses induced in all directions

c) thermal properties in all directions

d) density throughout

7. A material is known as allotropic or polymorphic if it

a) has a fixed structure under all conditions

b) exists in all crystal forms at different temperature

c) has its atoms distributed in random pattern

8. Pure iron is the structure of

a) ferrite

b) pearlite

c) cementite




9. The percentage of carbon in pig iron varies from

a) 1.5 to 2.5 %

b) 4 to 4.5 %

c) 0.1 to 1.0 %

10. Pig iron is the name given to

a) raw material for blast furnace

b) product of blast furnace made by reduction of iron ore

c) iron containing huge quantities of carbon

11. In grey cast iron, carbon is present in the form of

a) cementite

b) free carbon

c) flakes

12. Wrought iron is highly resistant to corrosion

a) true

b) false

13. Sulphur in pig iron tends to make it hard

a) true

b) false

14. Iron is

a) Paramagnetic

b) Ferromagnetic

15. Carbon steel is

a) an alloy of iron and carbon with varying quantities of phosphorous and sulphur

b) made by adding carbon in steel

c) extremely brittle

16. Nickel and chromium in steel help in raising the elastic limit and improve the resilience and ductility

a) false

b) true

17. Basic constituents of monal metal are




a) nickel, copper

b) zinc, tin and lead

18. German silver is an alloy of

a) silver

b) nickel, copper and zinc

19. Solder is an alloy consisting of

a) tin, antimony, copper

b) tin and lead

c) lead and copper

20. Steels are primarily designated according to

a) carbon content

b) alloying elements

21. Which of the following is an amorphous material

a) mica

b) glass

c) rubber

d) plastic

22. Stainless steels are most resistant to rusting and staining due to primarily to the presence of

a) Nickel

b) Chromium

c) Silicon

23. Chromium added to iron improves

a) fatigue resistance

b) corrosion resistance

c) high temperature resistance

d) none of the above

24. Which of the following is/are ceramic materials?

a) silica

b) glass




c) refractories

d) all the above

25. Duralium is an age hardenable Al-Zn-Mg alloy.

a) true

b) false

26. Alpha brass is more prone to dezincification in chloride atmosphere than beta brass.

a) true

b) false

27. For higher thermal shock resistance the thermal conductivity should be higher and thermal expansion should be lower.

a) true

b) false

28. Glass is a crystalline material.

a) true

b) false

---------- Key to Set 8 ----------

1. (a) (d)

2. (b)

3. (a)

4. (a)

5. (a)

6. (a)

7. (b)

8. (a)

9. (b)

10. (b)

11. (c)

12. (a)

13. (a)

14. (b)

15. (a)

16. (a)

17. (a)

18. (b)

19. (b)

20. (b)

21. (b)

22. (b)

23. (b)

24. (d)

25. (b)

26. (b)

27. (a)

28. (b)

MATERIAL SCIENCE & ENGINEERING AMIE

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Set 9: Polymers 1. The molecules in a polymer are held together by


a) Binary bonds

b) Secondary bonds

c) Strong bonds

d) Weak bonds

e) Covalent bonds

f) Vander walls or hydrogen bonds

2. The molecular weight of vinyl chloride is 62.5. Thus the molecular weight of a polyvinyl chloride with a degree of polymerization of 20,000 is

a) 320

b) 3.1 x 10-3

c) 1.25 x 106

d) 20,000

e) 62.5

3. Addition polymerization produces polymers with many cross links

a) true

b) false

4. Plasticizers

(two options)

a) Increase the melting point

b) depress the glass transition temperature

c) enhance cross linking

d) are generally organic liquids

e) are generally mono-atomic gases

5. This diagram illustrate (select two options)




a) the effect of plasticizers

b) the effect of heat on a thermosetting plastic

c) the process of aging

d) Cross linking formed by oxygen atoms

6. Thermosetting plastics will not deform when heated

a) true

b) false

7. polymers are

a) organic materials

b) inorganic materials

c) both

----------Key----------

1. (b) (d) (f)

2. (c)

3. (b)

4. (b) (d)

5. (c) (d)

6. (a)

7. (a)

Set 10: Electronic Properties of Materials 1. The conductivity of a metal is determined only by the number of valence electrons per atom

a) true

b) false

2. The Fermi level is

a) the highest occupied energy level at absolute zero of temperature




b) the average of the available energy levels

c) the highest available energy level

3. The valence electrons in a metal may be treated as an ‘electron gas’ because

a) they exert a pressure at the boundaries of the solid

b) there is a very large number of them

c) the kinetic energy of each electron is almost continuously variable

4. An applied electric field causes an electron gas cloud to

a) drift in the direction of field

b) drift in the direction opposite to the field

c) become smaller

5. Diamagnetic materials

a) are non magnetic

b) can not be magnetized

c) can be magnetized in one direction only

d) are magnetized in direction opposite to that of applied field

6. The resistivity of materials ranging from 1 to 100 ohm cm is known as

a) insulators

b) semiconductors

c) conductors

d) none of these

7. The SI units of electrical conductivity are

a) kg-3m-3s3A2

b) kgm-3s3A-2

c) ohm m

d) ohm-1m-3

8. The energy level difference between two successive levels for the lowest energy free electrons in order of magnitude

a) 1 eV

b) 10-33 J




c) 10-23 J

d) 10-19 J

9. The Fermi level EF depends on the length L of a linear solid as

a) 1/L2

b) 1/L3

c) 1/L

d) is independent of L

10. The classical equation for the kinetic energy can be used for the free electrons, because as compared to the velocity of light, their velocity is

a) more

b) slightly less

c) much less

d) zero

11. The magnetization of a superconductor is

a) 0

b) -B

c) -1

d) -H

12. Cold working of oxide superconductors is possible with

a) high hydrostatic pressure

b) moderate tensile stress

c) large tensile force

d) none of these

13. The room temperature electrical resistivity (ohm m) of the new oxide superconductors lies around

a) 10-9

b) 10-5

c) 107

d) 1018




14. The critical current density Jc that a superconductor can carry depends on (select three options)

a) T with respect to Tc

b) dislocation density

c) precipitate distribution

d) none of these

15. The fraction of electrons excited across the energy gap in Ge (Eg = 0.7 eV) at room temperature is

a) 0

b) 1.7 x 10-12

c) 2 x 10-12

d) 1.3 x 10-6

16. During an electron transition across the energy gap in Si,

a) the momentum of the electron changes

b) the direction of motion of the electron changes

c) the potential energy of the electron changes

d) the kinetic energy of the electron remains constant

e) all these

17. The energy gap in divalent metals is

a) very small

b) fairly small

c) zero

d) large

18. Pure silicon at 0 K is an

a) intrinsic semiconductor

b) extrinsic semiconductor

c) metal

d) insulator

19. In an extrinsic semiconductor, in the region where mobility variation with temperature is evident, the slope of log (conductivity) vs. 1/T plot is

a) positive




b) negative

c) 0

d) infinity

20. The two most common doping elements in Si are (select two options)

a) P

b) B

c) Sb

d) Bi

21. The majority charge carriers in p type Ge are

a) free electrons

b) ions

c) holes

d) conduction electrons

22. For lasting action, the energy gap of a semiconductor should be

a) direct gap

b) indirect gap

c) negative gap

d) gap > 5 eV

23. The function of an oxide layer during IC fabrication can be to


a) mask against diffusion or iron implant

b) insulate the surface electrically

c) produce a chemically stable surface

d) increase the melting point of silicon

24. The unit of magnetic permeability are


a) A m-1

b) Wb m-2

c) H m-1




d) Wb A-1 m-1

25. The total iron loss in a transformer core at 25 Hz and 50 Hz is 250 W and 800 W, respectively. The eddy current loss at 25 Hz is

a) 100 W

b) 150 W

c) 200 W

d) 600 W

26. A suitable material for audio and TV transformers is

a) ferrite

b) Fe - 4% Si

c) Fe - 30% Si

d) very pure Fe

----------Key----------

1. (b)

2. (a)

3. (c)

4. (b)

5. (d)

6. (b)

7. (a)

8. (b)

9. (d)

10. (c)

11. (d)

12. (a)

13. (b)

14. (a) (b) (c)

15. (d)

16. (e)

17. (c)

18. (d)

19. (a)

20. (a) (b)

21. (c)

22. (a)

23. (a) (b) (c)

24. (c) (d)

25. (b)

26. (a)

Short Question Answers 1. Define creep of metal.

2. What is cold working ?

3. Define `Burger’s vector’.




4. Which elements are to be used for doping silicon to make it a p-type semiconductor?

5. Define drift mobility of electrons in semi conducting materials.

6. What is meant by zone refining ?

7. State Matthiessen’s rule.

8. State Curie law for paramagnetic materials.

9. What are garnets ?

10. What is meant by a 'spinel’ ?

11. Why is cast iron used as a material for machine tool beds ?

12. When does Hook’s law appear to fall ?

13. Define the term `dislocation’.

14. What are the units of surface energy of a grain boundary ?

15. When is grain boundary shear possible in metals ?

16. Give two examples of heat resisting alloys.

17. If a tensile force of 10 N is applied to a specimen of length 100 mm, width 10 mm and thickness 1mm, what is the tensile stress developed in the specimen ?

18. Name the property by virtue of which the material can absorb maximum energy before the fracture takes place.

19. What is compressive strength of a material ?

20. Name the heat treatment process used for duralumin alloy.

21. What is the main objective of normalizing as a heat treatment process ?

22. What is the maximum solubility of carbon in iron ?

23. How are resistivity and conductivity related ?

24. Why does the resistivity of copper increase due to presence of solute atoms ?

25. What is the effect of the use of plasticizer on thermoplastic materials ?

26. What is the permeability of diamagnetic material ?

27. What are the constituents of white metal bearing alloys ?

28. What is 18-4-1 high speed steel.

29. Which alloying element is most important to make steel corrosion resistant ?

30. What is the carbon percentage in high-speed steel (W : Cr : V) ?




31. Cup and cone type of fracture is characteristics of which type of material ?

32. Which two parameters constitute slip system ?

33. What is the essential difference between brittle fracture and ductile fracture.

34. Is it possible to determine stress in a body without measuring corresponding strain ?

35. What is the essential difference between thermoplastic and thermoset polymers ?

36. What are the three stages of creep deformation ?

37. Polyvinyl chloride can exist in many stereo isomeric forms. Which form does not crystallize easily.

38. How many functional sites are present in divinyl benzene ?

39. Name the metal known to have highest electrical conductivity.

40. Which type of material shows necking phenomenon just before fracture and what is the common name for such a fracture ?

41. If we test a cast-iron sample in tensile mode, will there be any appreciable plastic deformation ? Why?

42. For which type of fracture, the direction of crack motion is very nearly perpendicular to the direction of the applied tensile stress ?

43. Which alloying element is most important to make steel corrosion resistant and what is the minimum percentage of this element required ?

44. Every plastic is polymer but every polymer may not be plastic. Is it true ? Justify.

45. What is the SI unit of modulus of elasticity ?

46. How would one increase the corrosion resistance of a cold rolled steel plate without painting or electroplating ?

47. What are the chemical names of any two of the following plastics ?

Teflon ; Perpex ; Terylene ; Bakelite

48. What is ductility and in what terms, is it measured ?

49. A test piece is 100 mm long. It is subjected to 0.2 % strain. What would be its length at this strain level ?

50. Which of the following materials would result in a cup-and-cone type fracture ?

Alumina ; Cast-iron ; Mild Steel ; Perspex

51. A brass plate contains a steel screw and it is being used in a marine environment. Which of the two metals would corrode faster and why ?

52. What is the weight % of carbon in low carbon steel ?

53. What is carburizing ?




54. Whether duralumin is wrought or cast alloy ?

55. Name at least two mechanisms of plastic deformation.

56. Which of the two main mechanism of plastic deformation requires greater shear stress to deform.

57. If you wound annealed MS and copper wire around our finger one of the two will not form a smooth circular.

58. Before cold working of AL alloy it is heated to about 5840C and then quenched or it should be heated to lower temperature 100 to 2000C and then air cooled ?

59. For which type of fracture, the direction of crack propagation is very nearly perpendicular to the direction of applied tensile stress ?

60. Brass and Bronze are the alloys of copper. What are the other constituents in these alloys ?

61. Suggest one suitable material for each of the following purpose with justifications:

(i) File cabinet

(ii) Water tap

(iii) Manhole cover

(iv) Garden chair

(v) Glass cutter

62. Atomic radii of two metal atoms are 0.128 nm and 0.133 nm respectively. Find out whether they form an solid solution, and if they form, state what type of solid solution it is.

63. Atomic radii of two metal atoms are 0.1278 nm (Cu) and 0.1431 nm (Al) respectively. Find out whether they form an solid solution, and if they form, state what type of solid solution it is.

64. Write down the slip plane and slip direction (one plane and one direction) of Nickel (only Miller indices). How many slip systems are there in Nickel?

65. Why has ferrite very low solubility of carbon, while austenite has high solubility of carbon?

66. Given an activation energy, Q of 142 kJ/mol, for the dilution of carbon in FCC iron and an initial temperature of 1000 K, find the temperature that will increase the diffusion coefficient by a factor 10. [ R = 8.314 J/(mol.K)]

67. A tension test recorded an engineering strain of 0.0046 against the engineering stress of 345 MPa of a material within its elastic range. Find out the elastic modulus of the material and the type of metallic alloy (like iron base etc.).

68. The final thickness of a hard copper sheet is 1.0 mm. It was produced by cold working with 25% deformation. What was the starting thickness of the metal before cold working?




69. The fracture toughness equation of a material is given by Kfc= σf√(π.a). If the material has a strength of 300 MPa, and a fracture toughness of 4 MPa√m, find out the largest internal crack in microns the material will support without cracking. σf = strength (MPa), a = crack size, m

70. Explain why ceramics are hard.

71. Name two important ceramic insulators with their properties.

72. Write the scientific names of following polymers with one of their typical use: Teflon, ABS

73. State the basic structural units of PMMA and Nylon 6,6 elaborating their properties.

74. What is E-Glass? Where it is commonly used?

75. What is Alnico?

76. Name two soft magnetic materials.

77. Which of the following materials shown in figure.

(a) the most ductile

(b) the most brittle

(c) the strongest

(d) the stiffest

78. Which of the following materials is the most ductile ?

Material Percentage elongation

80 - 20 brass 50

70 - 30 brass 70

60 - 40 brass 40

79. What are the two forms which carbon can take in cast iron and which type of iron does it produce ?

80. State whether low, medium or high carbon steel should be used for the following applications:

(a) heat - treated pin

(b) welded bracket

(c) guillotine blades

(d) forgings.




81. Why are cutting tools manufactured from high-carbon steel in preference to low or medium carbon?

82. Suggest whether low, medium or high-carbon steel should be used for the following applications.

(a) nails

(b) ball bearings

(c) car bodies

(d) crankshafts

(e) heat-treatable machine parts

(f) drills

83. State whether the carbon contents below relate to low, medium or high carbon steels.

(a) 0.29%

(b) 0.65%

(c) 0.87%

(d) 0.08%

(e) 1.32%

(f) 0.31%

(g) 0.59%

84. In which way does the normalising treatment differ from the annealing treatment.

85. Explain case hardening.

86. Give one example to show where normalising would be preferred to annealing, giving reasons to support your answer.

87. List any three applications of copper used in the home.

88. Explain why brass is not as good an electrical conductor as copper.

89. State the difference in composition of brass and bronze.

90. State two typical application for

(i) Copper

(ii) Brass

(iii) Bronze.

91. List six suitable application for aluminium alloys?




92. What is the disadvantage of using pure aluminium structurally?

93. Give the composition of solders having the following uses or applications:

(a) Plumber’s solder

(b) For soldering iron and steel

(c) For soldering tin cans.

94. Which of the following thermoplastics has the highest operating temperature?

(a) PVC

(b) Nylon

(c) PTFE

(d) Polystyrene.

----------Key----------

1. Creep is a slow deformation of an object loaded at a constant stress. It is also called as the time dependent past of the strain of a loaded member.

2. Cold working is the plastic deformation of a metal below its recrystallisation temperature. This increases the hardness and strength of the metal.

3. Burger’s vector is the displacement around a dislocation during plastic deformation. It is parallel to a screw dislocation and perpendicular to an edge dislocation.

4. Boron, Aluminium, Indium and Gallium.

5. Drift mobility is the drift velocity per unit field gradient. Or dimensionally it is given by m.sec-1/V m-1 = m2 V-1 sec.-1.

6. Zone refining is the process of separating impurities from a solid (crystals). It is done by first melting it and then solidifying at a controlled temperature. The solid phase separating in the beginning is purer than the liquid and the subsequent by solidifying portions. The purer phase is separated and the process is repeated to further remove the impurities. In case of silicon and germanium, after zone refining only one impurity atom can be left per 1010 atom of the solvent.

7. According to this rule the resistivity r of a conductor is given by r = rt + rr

Where, rt is the thermal part of the resistivity and rr is the residual resistivity due to solute atoms and other imperfections in the crystal.

8. This law states that the magnetic susceptibility is inversely proportional to the absolute temperature (T). It is expressed as C/T . Where the constant C is called curie constant.




9. garnets are non metallic soft magnetic material. These are usually prepared by powder compacting (sintering) process.

10. Spinels are compounds with two different cat ion A++ and B+++ and oxygen as the anion. A typical group of such materials are ferrites. These are ferromagnetic in nature.

11. Cast iron has good machinability, stable dimensions and has got the property of damping vibrations in machines tools.

12. Hooke’s law states that within elastic limit, for an elastic deformation, stress is proportional to strain. This does not hold in case of elastomers like rubber whose stress-strain behaviour is not linear in their elastic range.

13. It is a type of line imperfection in crystal in which positions of planes of atoms are missing or misaligned. These may be edge type or screw type.

14. Ergs/cm2 or dynes/cm.

15. Grain boundary shear is possible only at temperatures above 0.5 Tm where Tm is the melting point of the metal expressed in absolute scale.

16. (a) Thoria dispersed nickel.

(b) Jet alloy 1570 (0.22 %C, 20% Cr, 28% Ni and Rest Co.)

17. 1 N/mm2

18. The maximum energy absorbed before fracture is known as toughness.

19. The maximum compressive stress which can be developed in material under compressive load.

20. Duralumin is annealed.

21. In normalizing there is complete phase re-crystallization and fine grain structure is obtained.

22. Maximum solubility of carbon in iron is 2 %.

23. Conductivity of reciprocal of resistivity and has units ohm-1 m-1.

24. The solute atoms cause lattice distortion, these imperfections, cause irregularities in electric fields within the metal and decrease mean free path thus reducing mobility of electrons, thereby increasing resistivity of metal.

25. The plastisizer prevent crystallization producing non-crystalline solid. These provide flexibility, impart toughness, improve flow of material and act as internal lubricant.

26. The permeability of diamagnetic material is less than one.

27. The white metal bearing consists of Antimony, Copper, tin and lead typical examples are

(a) Antimony 7.5 %, Cu 4.5 %, Pb 0.75 %, rest Tin




(b) Antimony 10 %, Cu 0.5 %, Tin 0.5 %, Rest Lead

28. Steel having 18 % tungsten, 4% chromium, 1% vanadium with 0.75 % carbon is called 18-4-1 high speed steel.

29. Chromium is most important alloying element to make steel corrosion resistant.

30. The carbon percentage in high speed steel is about 0.75.

31. Cup and cone fracture is characteristic of moderately ductile material.

32. Slip plane and slip direction constitute slip system.

33. Little or no plastic deformation in brittle fracture and large plastic deformation in ductile fracture.

34. Yes by measuring force and area.

35. Thermoplastic polymer soften on heating while thermosetting sets or hardens.

36. Decreasing rate of strain, constant rate of strain and increasing rate of strain are three stages in creep deformation.

37. A tactic stereo tactic polyvinyl polymer chloride does not crystallize easily.

38. Poly functional.

39. Silver has highest electrical conductivity at normal temperature.

40. The ductile material shows necking phenomenon. The common name for such fracture is cup and cone fracture.

41. Very small plastic deformation is associated with tensile test of C.I. because it is brittle.

42. The direction of crack propagation is nearly perpendicular to applied tensile stress in Brittle fracture.

43. To shape steel corrosion resistant chromium is added with minimum 0.7%.

44. The statement is true.

45. The S.I. unit of modulus of elasticity is PASCAL (N/m2).

46. The corrosion resistance of a cold rolled steel plate can be increased by heat treatment or by making it cathode.

47. Teflon is polytetraflouroethylene (PTFE). Terylene is polyethylene tetrapthalate bakelite is phenyl formadelyde.

48. Ductility is the ability of being drawn into small section from large sections. This is measured by percentage elongation or percentage reduction.

49. 100.02 mm

50. steel is on the higher side of Galvanic series as compared to brass, so it will corrode faster.

51. The steel is on the higher side of Galvanic series as compared to brass, so it will corrode faster.




52. The percentage carbon in low carbon steel is 0.05 to 0.3.

53. Carburizing is diffusion or impregnation of carbon in the surface.

54. It is wrought alloy.

55. Slip and Twinning

56. Slip

57. Mild steel

58. They are heated to 5840C and the quenched.

59. Brittle type of fracture

60. Brass has other constituents; Zinc, Nickel and Lead Bronze has other constituents; Tin Phosphorous a nd Aluminium.

61. (i) Steel, board (ii) brass (iii) cast iron (iv) Wrough iron, concrete, bamboo, timber (v) Low alloy steel

62. They will form substitutional solid solution because size of atoms are nearly same.

63. Only 20% of copper atoms can be replaced by aluminium because there is a substantial difference in size.

64.

65. Ferrites has a lower packing factor. Each of the many interstitial sites is too small to accommodate even a small carbon atom. Only one carbon atom can be dissolved per 500 unit of cells of � ferrite. On the other hand, austenite accepts carbon atom interstitially. Since the carbon atom is small, the interstices in austenite can accommodate upto 10 a/o carbon. These small atoms reside in 1/2, 1/2, 1/2 sites.

66. Hint: D = D0 e-Q/RT

where D is diffusion coefficient, D0 is proportionality constant, Q is activation energy, T is temperature.

67. Hint: E = stress/strain, MPa → N/m2

68.

Hint:




where A0 and Af are original and final areas respectively.

69. Hint: 4MPa.√m = 300√(π.a.m)

70. Positive metallic ions (atoms that have lost electrons) and negative nonmetallic ions (atoms that have gained electrons) develop strong attractions for each other. Each cation (positive) surrounds itself with anions (negative). Considerable force is usually required to separate the two. Ceramic materials tend to be hard.

Ceramic materials are usually ionic or covalent bonded materials, and can be crystalline or amorphous. A material held together by either type of bond will tend to fracture before any plastic deformation takes place, which results in poor toughness in these materials. Additionally, because these materials tend to be porous, the pores and other microscopic imperfections act as stress concentrators, decreasing the toughness further, and reducing the tensile strength. These combine to give catastrophic failures, as opposed to the normally much more gentle failure modes of metals.

71. Alumina (Al2 O3 ): It is used in electrical insulator. It is used in spark plug. It is also used in computer circuits. It has high dielectric constant.

72. Teflon: PTFE (polytetrafluoroethylene)

ABS: Acrylonitrile - Butadiene - Styrene

Teflon-PTFE is a Polytetrafluoroethylene used in GoreTex and nonstick cookware, and also as a high-frequency, high temperature dielectric/insulator for electrical wires and coaxial cables.

ABS is an ideal material wherever superlative surface quality, colorfastness and luster are required. ABS is a two phase polymer blend. A continuous phase of styrene-acrylonitrile copolymer (SAN) gives the materials rigidity, hardness and heat resistance. The toughness of ABS is the result of submicroscopically fine polybutadiene rubber particles uniformly distributed in the SAN matrix.

73. PMMA: Polymethyl methacrylate

where 1 stands for H, 2 stands for H, 3 stands for CH3 and 4 stands for

Nylon 6/6: The polar C=O groups bond to the next chain through hydrogen bridges. This bonding favours a matching of adjacent molecules and leads to more complete crystallinity, than in polyethylene. Within crystals, the molecules are not kinked and coiled.




74. E-glass is fibre reinforced glasses, designed originally for electrical applications. They are most commonly calcium alumino borosilicate glasses that contain no Na+ ions.

75. Alnico Magnet: This permanent magnet, which contains aluminium, nickel and cobalt in an iron base alloy is magnetized as a single phase, then is heat treated to provide, very fine grained, two phase microstructure.

76. Pure iron, Silicon ferrite, Peralloy (Ni-fe), Superpermalloy (Ni-Fe-Mo)

Soft magnetic materials are those materials that are easily magnetised and demagnetised.

77. (a) Material C

(b) Material B

(c) Material A

(d) Material A.

78. The most ductile material is the one with the largest percentage elongation, i.e. the 70 - 30.

79. Cementite - producing ‘white’ iron

Graphite - producing ‘grey’ iron.

80. (a) Medium

(b) Low

(c) High

(d) Medium or low.

81. High carbon steels contain more carbon and are therefore harder both initially and after heat treatment. In most instances the cutting tool must be harder than the material being cut.

82. (a) Low

(b) High

(c) Low

(d) Medium

(e) Medium

(f) High.

83. (a) Low

(b) High

(c) High

(d) Low




(e) High

(f) Medium

(g) Medium

84. The only difference between annealing and normalising treatments is the way in which they are cooled. Material which is being annealed is cooled in the furnace whilst for normalising cooling is done in still air.

85. Case-hardening is a method of hardening a ferrous alloy so that the outer portion, or case is made substantial harder than the inner portion or core. Its purpose is to produce a material which can resist abrasion and wear due to the hard surface and resist shock loading due to the softer core.

86. The main reason for preferring normalizing to annealing a ferrous material is when improved machinability is desired. A material in its softest state is not necessarily in its most machinable state. To facilitate machining the material must allow chip cracks to propagate and not spread on the too; point. Annealing a ferrous material produces a soft material which may not machine as easily as a normalized steel.

87. Typical application include: domestic water tanks, rubbing for central heating, ornamental canopies above fires, jugs, vases.

88. The addition of zinc to produce brass, together with other elements and impurities, drastically reduces the conductivity of the material.

89. Both are alloys of copper. Brass is mainly a combination of copper and zinc, whereas bronze is an alloy of copper and tin. Each can contain other elements in smaller quantities.

90. Typical application include

Copper - electrical conductors, pipes, architectural cladding, boiler tubes.

Brass - jewellery, presswork and marine applications

Bronze - bearings (light and heavy duty), pumps, valves, etc. coins.

91. Aircraft parts - engine and frame, marine applications, rivets, radiators, gearboxes, sumps, scaffold tubes, cooking utensils, decorative paneling etc.

92. It is very weak.

93. (a) 33% tin, 67% lead

(b) 12% tin, 80% lead, 8% antimony

(c) 40% tin, 60% lead.

94. PTFE

40872180 Material Science Objective Questions

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