761. Damage to metal surface by mechanical action is called
A. Pitting
B. Corrosion
C. Erosion
D. None of these
✅ The correct answer is option C.
Chemical Engineering
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762. In a casting, cold shut defect is caused by
A. Low pounhg temperature
B. Melt-mould reactions
C. Faulty gating system
D. Very low mould permeability
✅ The correct answer is option A.
763. The stress at which a metal fails by fatigue lies
A. Near the fracture point of the stress-strain curve
B. In the plastic range
C. In the elastic range
D. None of these
✅ The correct answer is option C.
764. A material in which the atoms are arranged regularly in some directions but not in others, is termed as ‘mesomorphous material’; an example of which is
A. Lead
B. Glass
C. Mica
D. Silver
✅ The correct answer is option A.
765. Fibre glass is a composite material of
A. Glass fibre in a polymer matrix
B. Glass fibre in a metallic matrix
C. Polymer fibre in a glassy matrix
D. Both B & C
✅ The correct answer is option A.
766. Austempering of steel requires.it to be heated to 875°C followed by sudden cooling to 250-525°C, thereby changing austenite to
A. Sorbite
B. Bainite
C. Martensite
D. Troostite
✅ The correct answer is option B.
767. Diamagnetic materials
A. Are magnetised by eddy currents only
B. Are non-magnetic and can not be magnetised
C. Are magnetised in direction opposite to the magnetic field
D. Can be magnetised in one direction only
✅ The correct answer is option C.
768. __________ number determines whether the fluid flow in an open channel is supercritical, critical or sub-critical.
A. Mach
B. Reynolds
C. Froude
D. Weber
✅ The correct answer is option C.
769. What is the critical radius of insulation (cms) for a metallic cylinder, if the convective heat transfer co-efficient with the ambient atmosphere is 5 W/m². °K ? Thermal conductivity of metal and insulation material are 40 and 0.1 W/m.°K respectively.
A. 2
B. 5
C. 10
D. 20
✅ The correct answer is option A.
770. __________ is the trade name assigned to a non-ferrous cast alloy composed of cobalt, chromium & tungsten.
A. Stellite
B. High speed steel
C. Cermet
D. Alnico
✅ The correct answer is option A.