Mechanical Engineering MCQs

Page No. 149

Depending on the radiating properties, a body will be opaque when _________________?


ap = 0, x = 0 and a = 1


bp=l,x = 0anda = 0


cp = 0, x = 1 and a = 0


dx – 0, a + p = 1


View Answer x – 0, a + p = 1

Depending on the radiating properties, a body will be white when_________________?


ap = 0, x = 0 and a = 1


bp=l,T = 0anda = 0


cp = 0, x = 1 and a = 0


dx = 0, a + p = 1


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

The ratio of the emissive power and absorptive power of all bodies is the same and is equal to the emissive power of a perfectly black body. This statement is known as_________________?


aKrichoff’s law


bStefan’s law


cWien’ law


dPlanck’s law


View Answer Krichoff’s law

The thermal diffusivities for solids are generally__________________?


aless than those for gases


bjess than those for liquids


cmore than those for liquids and gases


dmore or less same as for liquids and gases



According to Stefan’s law, the total radiation from a black body per second per unit area is proportional to____________________?


aabsolute temperature


bT2


cT5


dt


View Answer t

Depending on the radiating properties, a body will be black when_________________?


ap = 0, x = 0 and a = 1


bp= l,T = 0anda = 0


cp = 0, x = 1 and a = 0


dx = 0, a + p = 0



The total emissivity power is .defined as the total amount of radiation emitted by a black body per unit_______________?


atemperature


bthickness


carea


dtime


View Answer time

40% of incident radiant energy on the surface of a thermally transparent body is reflected back. If the transmissivity of the body be 0.15, then the emissivity of surface is____________________?


a0.45


b0.55


c0.40


d0.75


View Answer 0.45

The emissive power of a body depends upon its___________________?


atemperature


bwave length


cphysical nature


dall of the above


View Answer all of the above

The ratio of the energy absorbed by the body to total energy falling on it is called_________________?


aabsorptive power


bemissive power


cabsorptivity


demissivity


View Answer absorptive power

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