What is the equivalent emissivity for radiant heat exchange between a small body (emissivity = 0.in a very large enclosure (emissivity = 0.5)?
a) 0.5
b) 0.4
c) 0.2
d) 0.1
Q.2.
If a body is at 2000K, the wavelength at which the body emits maximum amount of radiation is __________
a) 1.45µm
b) 1.45cm
c) 0.345cm
d) 0.345µm
Q.3.
Which of the following parameter is not responsible for loss of heat from a hot surface in room?
a) Temperature of the surface
b) Emissivity of the surface
c) Temperature of the air in the room
d) Dimensions of the room
Q.4.
Hot coffee in a cup is allowed to cool. Its cooling rate is measured and found to be greater than the value calculated by conduction, convection and radiation measurement. The difference is due to:
a) Properties of coffee changing with temperature
b) Currents of air flow in the room
c) Underestimation of the emissivity of coffee
d) Evaporation
Q.5.
Which of the following statement is incorrect?
a) For metals, the value of absorptivity is high
b) For non-conducting materials, reflectivity is low
c) For polished surfaces, reflectivity is high
d) For gases, reflectivity is very low
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