During the optical excitation of carriers in a semiconductor, the minimum energy re‐ quired to form free carriers is called the band gap. The energy below that value cannot excite free carriers. However, low-temperature absorption studies of semiconductors have shown excitation just below the band gap [1]. This excitation is associated with the formation of…
1.What is the maximum use of magnesium ? Ans: Magnesium is used to alloy with aluminium and as an additive for making SG (Spheroidal Graphite) iron. 2.What for zinc finds applications ? Ans: Galvanizing consumes the largest proportion of zinc. Zinc is resistant to corrosion but is attacked by acids and alkalies. Zinc alloy.s are…
1.What do you understand by eutectic ? Ans: It is mechanical mixture of two or more phases which solidify simultaneously from the liquid alloy. 2.Explain the difference between grey iron and white iron. What is mottled iron ? Ans: The carbon in cast iron could exist at room temperature as either iron carbide, or as…
1.Define buckling factor. Ans: It is the ratio of the equivalent length of column to the minimum radius of gyration. 2.What do you understand by catenary cable ? Ans: A cable attached to the supports and carrying its own weight. 3.What is coaxing ? Ans: It is the process of improving fatigue properties by first…
1.What is the structure of pure iron and whether it is soft or hard ? Ans: Ferrite and it is soft. 2.Which elements increase the corrosion resistance of steel ? Ans: Chromium and nickel. 3.What causes hardness in steel ? How heat treatment alters properties of steel ? Ans: The shape and distribution of the…
1.Explain the difference between ferrite, austenite and graphite ? Ans: Ferrite is the solid solution of carbon and other constituents in alpha-iron. It is soft, ductile and relatively weak. Austenite is the solid solution of carbon and other constituents in gamma-iron. It exists in ordinary steels at elevated temperatures, but it is also found at…
1.For which parts the Wahl factor and Lewis form factor used ? Ans: For springs and gears respectively. 2.How oxygen can be removed from steel during melting? What are fully killed steels ? Ans: Oxygen can be removed by adding elements such as manganese, silicon or aluminium which, because of their high affinity for oxygen,…
1.What does thermal diffusivity of metals signify. Ans: Thermal diffusivity is associated with the speed of propagation of heat into solids during changes in temperature with time. 2.For conduction of heat, the instantaneous rate of heat flow is product of three factors. What are these ? Ans: (i) Area of the section of the heat flow…
1.Which element is added in steel to increase resistance to corrosion ? Ans: Chromium. 2.Whether individual components in composite materials retain their characteristics or not? Ans: yes. 3.An elastomer is a polymer when its percentage elongation rate is ? Ans: Greater than 100%. 4.If percentage elongation of a material is more than 200%, it is…
1.What is the difference between isotropic and anisotropic materials ? Ans: If a material exhibits same mechanical properties regardless of loading direction, it is isotropic, e.g., homogeneous cast materials. Materials lacking this property are anisotropic. 2.What are orthotropic materials ? Ans: It is a special class of anisotropic materials which can be described by giving…