Mechanical Engineering MCQs

Page No. 150

The amount of radiation mainly depends on___________________?


anature of body

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btemperature of body

✖


ctype of surface of body

✖


dall of the above

✓


View Answer all of the above

Absorptivity of a body will be equal to its emissivity___________________?


aat all temperatures

✖


bat one particular temperature

✖


cwhen system is under thermal equi-librium

✓


dat critical temperature

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Depending on the radiating properties, body will be transparent when________________?


ap = 0, x = 0 and a = 1

✖


bp=l,x = 0,anda = 0

✖


cp = 0, T= l,anda = 0

✓


dX = 0, a + p = 1

✖


View Answer p = 0, T= l,anda = 0

Two plates spaced 150 mm apart are maintained at 1000°C and 70°C. The heat transfer will take place mainly by ___________________?


aconvection

✖


bfree convection

✖


cforced convection

✖


dradiation

✓


View Answer radiation

In regenerator type heat exchanger, heat transfer takes place by___________________?


adirect mixing of hot and cold fluids

✖


ba complete separation between hot and cold fluids

✖


cflow of hot and cold fluids alternately over a surface

✓


dgeneration of heat again and again

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If the temperature of a solid surface changes form 27°C to 627°C, then its emissive power changes in the ratio of___________________?


a3

✖


b6

✖


c9

✖


d81

✓


View Answer 81

A perfect black body is one which_______________?


ais black in colour

✖


breflects all heat

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ctransmits all heat radiations

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dabslprbs heat radiations of all wave lengths falling on it

✓



Planck’s law holds good for________________?


ablack bodies

✓


bpolished bodies

✖


call coloured bodies

✖


dall of the above

✖


View Answer black bodies

A grey body is one whose absorptivity _________________?


avaries with temperature

✖


bvaries with the wave length of incident ray

✖


cvaries with both

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ddoes not vary with temperature and wave length of the incident ray

✓



The thermal diffusivities for gases are generally_____________________?


amore than those for liquids

✓


bless than those for liquids

✖


cmore than those for solids

✖


ddependent on the viscosity

✖



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