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Engineering Materials

Subject : engineering
Instructions:
  • Answer 50 questions in 15 minutes.
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  • Match each statement with the correct term.
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This is a study tool. The 3 wrong answers for each question are randomly chosen from answers to other questions. So, you might find at times the answers obvious, but you will see it re-enforces your understanding as you take the test each time.
1. The Magnetization of the material - and is essentially the dipole moment per unit volume. It is proportional to the applied field. Xm is the magnetic susceptibility.






2. 1. Insulators: Higher energy states NOT ACCESSIBLE due to gap 2. Semiconductors: Higher energy states separated by a smaller gap.






3. Transformer cores require soft magnetic materials - which are easily magnetized and de-magnetized - and have high electrical resistivity - Energy losses in transformers could be minimized if their cores were fabricated such that the easy magnetizatio






4. These materials are "attracted" to magnetic fields.






5. Liquid polymer at room T - sandwiched between two sheets of glass - coated with transparent - electrically conductive film. - Character forming letters/ numbers etched on the face - Voltage applied disrupts the orientation of the rod- shaped molecule






6. The ability of a material to absorb heat - Quantitatively: The energy required to produce a unit rise in temperature for one mole of a material.






7. 1. Imperfections increase resistivity - grain boundaries - dislocations - impurity atoms - vacancies 2. Resistivity - increases with temperature - wt% impurity - and %CW






8. Flaws and Defects - They concentrate stress locally to levels high enough to rupture bonds.






9. Different orientation of cleavage planes in grains.






10. Becomes harder (more strain) to stretch (elongate)






11. Undergo little or no plastic deformation.






12. Growing interconnections to connect devices -Low electrical resistance - good adhesion to dielectric insulators.






13. ...occurs in bcc metals but not in fcc metals.






14. Increase temperature - no increase in interatomic separation - no thermal expansion






15. - Metals that exhibit high ductility - exhibit high toughness. Ceramics are very strong - but have low ductility and low toughness - Polymers are very ductile but are not generally very strong in shear (compared to metals and ceramics). They have low






16. Rho=F/A - tau=G/A . Depending on what angle the force is applied - and what angle the crystal is at - it takes different amounts of force to induce plastic deformation.






17. This strength parameter is similar in magnitude to a tensile strength. Fracture occurs along the outermost sample edge - which is under a tensile load.






18. Increase temperature - increase in interatomic separation - thermal expansion






19. (sigma)=K(sigma)^n . K = strength coefficient - n = work hardening rate or strain hardening exponent. Large n value increases strength and hardness.






20. The magnetic hysteresis phenomenon: Stage 1: Initial (unmagnetized state) Stage 2: Apply H - align domains Stage 3: Remove H - alignment remains => Permanent magnet Stage 4: Coercivity - Hc negative H needed to demagnitize Stage 5: Apply -H - align d






21. Measures Hardness 1. psia = 500 x HB 2. MPa = 3.45 x HB






22. Allows you to calculate what happened G=F' x cos(lambda) - F=F' x cos(phi)






23. Transmitted light distorts electron clouds - The velocity of light in a material is lower than in a vacuum - Adding large ions to glass decreases the speed of light in the glass - Light can be "bent" (or refracted) as it passes through a transparent






24. Because of ionic & covalent-type bonding.






25. A measure of the ease with which a B field can be induced inside a material.






26. Ohms Law: voltage drop = current * resistance






27. Occurs at a single pore or other solid by refraction n = 1 for pore (air) n > 1 for the solid - n ~ 1.5 for glass - Scattering effect is maximized by pore/particle size within 400-700 nm range - Reason for Opacity in ceramics - glasses and polymers.






28. A parallel-plate capacitor involves an insulator - or dielectric - between two metal electrodes. The charge density buildup at the capacitor surface is related to the dielectric constant of the material.






29. Emitted light is in phase






30. The ability of a material to be rapidly cooled and not fracture






31. Elastic means reversible! This is not a permanent deformation.






32. Hardness is the resistance of a material to deformation by indentation - Useful in quality control - Hardness can provide a qualitative assessment of strength - Hardness cannot be used to quantitatively infer strength or ductility.






33. A high index of refraction (n value) allows for multiple internal reactions.






34. 1. Ductility- % elongation - % reduction in area - may be of use in metal forming operations (e.g. - stretch forming). This is convenient for mechanical testing - but not very meaningful for most deformation processing. 2. Toughness- Area beneath str






35. Light Amplification by Stimulated Emission of Radiation






36. Diffuse image






37. Occur when lots of dislocations move.






38. 1. Tensile (opening) 2. Sliding 3. Tearing






39. # of thermally generated electrons = # of holes (broken bonds)






40. 1. Tc= critical temperature- if T>Tc not superconducting 2. Jc= critical current density - if J>Jc not superconducting 3. Hc= critical magnetic field - if H > Hc not superconducting






41. With Increasing temperature - the saturation magnetization diminishes gradually and then abruptly drops to zero at Curie Temperature - Tc.






42. Stress concentration at a crack tips






43. Undergo extensive plastic deformation prior to failure.






44. 1. Hard disk drives (granular/perpendicular media) 2. Recording tape (particulate media)






45. Specular: light reflecting off a mirror (average) - Diffuse: light reflecting off a white wall (local)






46. These are liquid crystal polymers- not your normal "crystal" -Rigid - rod shaped molecules are aligned even in liquid form.

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47. Impurities added to the semiconductor that contribute to excess electrons or holes. Doping = intentional impurities.






48. Heat capacity.....- increases with temperature -for solids it reaches a limiting value of 3R






49. Occur due to: restrained thermal expansion/contraction -temperature gradients that lead to differential dimensional changes sigma = Thermal Stress






50. Without passing a current a continually varying magnetic field will cause a current to flow