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141.

The rate of radiant energy, which is emitted by a surface at any temperature and in small wavelengths is found from the known rate of energy, which under the same conditions would be emitted from a black surface, by multiplying with the absorptivity. Above enunciation is known as

A.	Planck's law	B.	Kirchhoff's law
C.	Stefan Bolzmann's law	D.	Lambart's rule
E.	None of the above

142.

A surface which diffusely reflects and emits tha same amount of energy which it receives by radiation, is known as

A.	A perfect surface	B.	A perfect grey surface
C.	A perfect white surface	D.	A perfect radiating surface
E.	None of the above

143.

1 micron is equivalent to

A.	10-2 cm	B.	10-3 cm
C.	10-4 cm	D.	10-6 cm
E.	None of the above

144.

Planck's law of radiation is applicable to

A.	Radiation of any kind	B.	Temperature radiation
C.	Monochromatic radiation	D.	Thermal radiation
E.	None of the above

145.

Which rays have the least wavelength?

A.	Infra-red	B.	Ultraviolet
C.	Radio	D.	X-rays
E.	Cosmic rays

146.

The total radiant energy emitted by a plane surface per unit area and unit time is called

A.	Radiant flux density	B.	Total absorptivity
C.	Radiant energy	D.	Radiant intensity
E.	None of the above

147.

A perfect black body is

A.	Black in colour	B.	One which absorbs total radiant energy
C.	One which does not reflect the radiant energy	D.	One through which radiant energy is not transmitted
E.	One which absorbs all radiant energy at all wavelengths

148.

Identify the correct statement

A.	Bodies black in colour are known as black bodies in radiation	B.	Only some substances emit radiation
C.	Quality and quantity of radiation depends on the properties of the material only	D.	A substance will emit radiation at a particular wavelength only
E.	All substances emit radiation the quality and quantity depends on the absolute temperature and properties of the material composing the radiating body

149.

Wavelength is generally measured in

A.	km	B.	m
C.	cm	D.	mm
E.	microns

150.

A liquid flowing through a tube is turbulent. In which case will the maximum change in heat transfer coefficient occur?

A.	Diameter of the tube is increased 2 times maintaining the velocity of flow constant	B.	Diameter of the tube is increased 2 times maintaining the rate of liquid flow constant
C.	Diameter of the tube is increased 4 time maintaining the ratio of liquid flow constant	D.	Diameter of the tube is increased 4 times maintaining the velocity of flow constant