Maximum heat dissipation occurs from a steel wire (k = 0.5 W/m. k) of 15 mm diameter exposed to air (h = 20W/m2 .k), when the insulation thickness is __________ mm.
15
25
10
30
Correct Answer :
B. 25
Related Questions
Which of the following is an unconventional source of energy?
Thermal power
Hydroelectric power
Nuclear-fusion power
Solar power
Change in volume of metals from absolute zero temperature to their melting points is
Almost same for all metals
Different for different metals
Less for low melting point metals
Less for high melting point metals
The heat released by cooling one mole of copper from 400 K to room temperature (300 K) is (assume : Cp of copper is 23 J K-1mole-1)
2300 J
4600 J
230 J
2.3 × 106 J
With increase in annealing temperature, the following defect density decreases.
Vacancy
Dislocation
Grain boundary
All of these
Joule-Thomson co-efficient is the ratio of
Pressure change to temperature change occuring during adiabatic compression of a gas
Pressure change to temperature change occuring during adiabatic throttling of a gas
Temperature change to pressure change occuring during adiabatic compression of a gas
Temperature change to pressure change occuring during adiabatic throttling of a gas
Brittleness induced due to the presence of sulphur in steel can be reduced by adding
Manganese
Magnesium
Vanadium
Copper
Co-efficient of performance of a Carnot cycle refrigerator operating between - 23°C and + 27°C is
3
5
0.5
1.5
Brazing filler metal used for joining steel plates
Melts below the melting points of base metals
Melts below 300°C
Is copper phosphorous alloy
Is copper
Optical activity is a/an __________ property.
Additive
Constitutive
Both (A) & (B)
Neither (A) nor (B)
Wrought iron is not
Ductile & resistant to corrosion/rusting
Weldable easily
Having uniform strength in all directions
Having maximum tensile strength along the lines of slag distribution
What is the percentage of chromium in 18-4-1 high speed steel?
1
4
18
23
Fatigue limit improvement by over stressing the metal by successively increasing the load is called coaxing. In fatigue failure, the material fails
Below the yield point
Above the yield point
Below the elastic limit
At the elastic limit
The ratio of the shear stress to the principal stress on a principal plane is
0
1
1/2
1/3
Pick out the wrong statement.
Ductile fracture of a stressed material, which exhibits a large plastic deformation is commonly caused by the formation and coalescence of voids in the necked region
Brittle fracture is caused by the propagation of pre-existing cracks in the material and involves minimum plastic deformation
Fatigue fracture of a material is always brittle in nature and takes place due to the existence of line imperfections
Brittle materials are generally tested in tension
Parallel straight line pattern of temperature distribution for both hot and cold fluids is observed in case of heat exchanger of the type
Parallel flow with equal heat capacities
Counter flow with equal heat capacities
Counter flow with unequal heat capacities
Parallel flow with unequal heat capacities
Out of the following the refractive index is the highest for
Glass
Diamond
Brine
Kerosene
Difference at any instant between the value of the controlled variable and the set point is called the
Deviation
Derivative time
Error ratio
Differential gap
While the bin cards are used in the effective stores management, the queuing theory is associated with the __________ time.
Waiting
Idle
Inspection
Tool replacement
Water-tube boiler is the one, in which
Water passes through tubes and flue gases around it
Tube carrying hot flue gases are immersed in a pool of water
Tubes are placed in vertical position
None of these
Machinability of hard alloys and tool steels is improved by
Spheroidising
Annealing
Tempering
Normalising
Alloy powder manufactured by the following process have spherical shapes.
Electrochemical deposition
Gaseous reduction
Atomisation
Mechanical attrition
While the oxy-acetylene flame produces a temperature of 3200°C, the temperature produced by oxy-hydrogen flame is about __________ °C.
1800
2000
2400
3000
Wave length of X-rays is about 1 angstrom; however it cannot pass through a sheet of
Paper
Cloth
Lead
Aluminium
Thermal equivalent of electrical power in practical calculation is __________ kcal/kWh.
746
3000
1000
550
Plants produce carbohydrates from the CO2 present in the atmosphere by
Polymerisation
Photochemical reaction
Oxidation
None of these
__________ is the hardest material out of the following.
Boron carbide
Tungsten carbide
Hardened steel
Silicon carbide
A 2 kg object weighs 1.8 kgf on a spring balance. The value of 'g' at that location in m/sec2 is
8.82
9.81
10.88
0.95
Titanium is added to molten aluminium alloys before casting for the purpose of
Grain refinement
Increasing corrosion resistance
Reducing porosity
Improving fluidity
Addition of __________ to steel does not help in improving its machinability.
Sulphur
Silicon
Lead
Phosphorous
Which of the following does not discharge the dust collected as a dry solid?
Electrostatic precipitator
Wet scrubber
Bag filter
Gravity settling chamber