971. A material is said to be allotropic, if it has
A. fixed structure at all temperatures
B. atoms distributed in random pattern
C. different crystal structures at different temperatures
D. any one of the above

972. Closed packed hexagonal space lattice is found in
A. zinc, magnesium, cobalt, cadmium, antimony and bismuth
B. gamma-iron, aluminium, copper, lead, silver and nickel
C. alpha-iron, tungsten, chromium and molybdenum
D. none of the above

973. The hardness and tensile strength in austenitic stainless steel can be increased by
A. hardening and cold working
B. normalising
C. martempering
D. full annealing

974. The wet bulb temperature during sensible heating of air
A. remains constant
B. increases
C. decreases

975. In free convection heat transfer transition from laminar to turbulent flow is governed by the critical value of the
A. Reynold’s number
B. Grashoff’s number
C. Reynold’s number, Grashoff’s number
D. Prandtl number, Grashoff’s number

976. An alloy steel which is work hardenable and which is used to make the blades of bulldozers, bucket wheel excavators and other earth moving equipment contain iron, carbon and
A. chromium
B. silicon
C. manganese
D. magnesium

977. Which of the following has a fine gold colour and is used for imitation jewellery?
A. Silicon bronze
B. Aluminium bronze
C. Gun metal
D. Babbit metal

978. When the steel is normalised, its
A. yield point increases
B. ductility decreases
C. ultimate tensile strength increases
D. all of these

979. In a refrigerating machine, heat rejected is __________ heat absorbed.
A. equal to
B. less than
C. greater than

980. Silicon when added to copper improves
A. machinability
B. hardness
C. hardness and strength
D. strength and ductility

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