Engineering :: Heat Transfer

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71.

a micron is equal to

A.	10-4 metres	B.	10-5 metres
C.	10-6 metres	D.	10-8 metres
E.	10-12 metres

72.

If the absorptivity plus reflectivity of a body equals 1, then the body is known as

A.	Black body	B.	Grey body
C.	Opaque body	D.	White body
E.	None of the above

73.

Gases have poor

A.	Reflectivity	B.	Absorptivity
C.	Transmissivity	D.	Absorptivity + transmissivity
E.	Reflectivity + absorptivity

74.

All substances emit radiation, the quality and quantity depending upon the absolute temperature and the properties of the material composing the radiating body. The above statement is known as the statement of

A.	Planck's law	B.	Kirchhoff's law
C.	Stefan-Bolzmann's law	D.	Law of radiation
E.	D Alambert's rule

75.

The relation between the emissive and absorptive power of a surface is developed under

A.	Planck's law	B.	Kirchhoff's law
C.	Electrical analogy	D.	Stefan-Baltzmann's law
E.	Law of radiations

76.

For all substances the absorptivity must lie between

A.	0 and 0.1	B.	?1 and +1
C.	?0.5 and + 0.5	D.	0 and 1
E.	0 and + 0.5

77.

Which one of the following approximates to the black body condition?

A.	Ice	B.	Water
C.	Lamp black	D.	All of the above
E.	None of the above

78.

Which one of the following will radiate heat to a large extent?

A.	White polished surface	B.	White rough surface
C.	Black rough surface	D.	Black polished surface

79.

Two bodies one hot and the other cold are kept in vacuum. What will happen to the temperature of the hot body after sometime?

A.	Remains the same	B.	Decreases due to convection
C.	Increases due to convection	D.	Increases due to radiation
E.	Decreases due to radiation

80.

A body cools from 90?C to 80?C in 5 minutes. Under the same external conditions to cool from 80?C to 70?C the body will take

A.	5 minutes	B.	4 minutes
C.	2.5 minutes	D.	More than 5 minutes
E.	Cannot be predicted