If the reflectivity of an opaque surface is 0.6, then emissivity of that surface will be

• 0

• 1

• 0.6

• 0.4

• can't be determined

Stefan Boltzmann Law estimate

• spectral emissive power of any body

• hemispherical emissive power of any body

• total hemispherical emissive power of any body

• None of these are correct

A light bulb of filament temperature 2400K will emit maximum power at which wavelength. This problem can be solved by

• Plank's Law

• Stefan Boltzmann Law

• Wein Law

• Kirchoff's law

reflectivity of a black body is

• 0

• 1

• between 0 and 1

• None of these

For a black body

• Radiosity =Emissive power

• Radiosity< Emissive power

• Radiosity> Emissive power

• There is no relation between Radiosity & Emissive power

For a gray surface

• radiation properties are independent of wave length

• radiation properties are independent of direction

• emissivity =absorptivity=1

• emissivity is not equal to absorptivity

Radiation properties can be changed by a thin coating on them

• True

• False

A black body is a diffuse emitter

• True

• False

Value of Stefan Boltzmann Constant in SI unit is 

• $5.87\times10^8$

• $5.67\times10^8$

• $7.65\times10^8$

• None of these

Emissivity of concrete is close to

• 0

• 1