Mechanical Engineering MCQs

Page No. 151

Thermal diffusivity of a substance is __________________?


adirectly proportional to thermal con¬ductivity

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binversely proportional to density of substance

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cinversely proportional to specific heat

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dall of the above

✓


View Answer all of the above

Stefan Boltzmann law is applicable for heat transfer by __________________?


aconduction

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bconvection

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cradiation

✓


dconduction and radiation combined

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View Answer radiation

The unit of Stefan Boltzmann constant is ____________________?


awatt/cm2 °K

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bwatt/cm4 °K

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cwatt2/cm °K4

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dwatt/cm2 °K4

✓


View Answer watt/cm2 °K4

Log mean temperature difference in case of counter flow compared to parallel flow will be________________?


asame

✖


bmore

✓


cless

✖


ddepends on other factors

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View Answer more

According to Stefan-Boltzmann law, ideal radiators emit radiant energy at a rate proportional to___________________?


aabsolute temperature

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bsquare of temperature

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cfourth power of absolute temperature

✓


dfourth power of temperature

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In free con-vection heat transfer, Nusselt number is function of________________?


aGrashoff no. and Reynold no

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bGrashoff no and Prandtl no.

✓


cPrandtl no. and Reynold no

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dGrashoff no., Prandtl no and Reynold no

✖



Which of the following property of air does not increase with rise in temperature ________________?


athermal conductivity

✖


bthermal diffusivity

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cdensity

✓


ddynamic viscosity

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View Answer density

The energy distribution of an ideal reflector at higher temperatures is largely in the range of ___________________?


ashorter wavelength

✓


blonger wavelength

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cremains same at all wavelengths

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dwavelength has nothing to do with it

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View Answer shorter wavelength

The value of Prandtl number for air is about _______________________?


a0.1

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b0.3

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c0.7

✓


d1.7

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View Answer 0.7

Total emissivity of polished silver compared to black body is___________________?


asame

✖


bhigher

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cmore or less same

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dvery much lower

✓


View Answer very much lower

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