A. at all temperatures
B. at one particular temperature
C. when system is under thermal equi-librium
D. at critical temperature
E. for a polished body
Related Mcqs:
- According to Kirchoff’s law, the ratio of emissive power to absorptivity for all bodies is equal to the emissive power of a _________________?
A. grey body
B. brilliant white polished body
C. red hot body
D. black body
E. none of the above - A grey body is one whose absorptivity _________________?
A. varies with temperature
B. varies with the wave length of incident ray
C. varies with both
D. does not vary with temperature and wave length of the incident ray
E. there is no such criterion - 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_________________?
A. Krichoff’s law
B. Stefan’s law
C. Wien’ law
D. Planck’s law
E. Black body law - When heat is transferred form hot body to cold body, in a straight line, without affecting the intervening medium, it is referred as heat transfer by __________________?
A. conduction
B. convection
C. radiation
D. conduction and convection
E. convection and radiation - Emissivity of a white polished body in comparison to a black body is________________?
A. higher
B. lower
C. same
D. depends upon the shape of body
E. none of the above - 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____________________?
A. 0.45
B. 0.55
C. 0.40
D. 0.75
E. 0.60 - The amount of heat flow through a body by conduction is_______________?
A. directly proportional to the surface area of the body
B. directly proportional to the temperature difference on the two faces of the body
C. dependent upon the material of the body
D. inversely proportional to the thickness of the body
E. all of the above - Depending on the radiating properties, body will be transparent when________________?
A. p = 0, x = 0 and a = 1
B. p=l,x = 0,anda = 0
C. p = 0, T= l,anda = 0
D. X = 0, a + p = 1
E. a = 0,x + p= 1 - The ratio of the energy absorbed by the body to total energy falling on it is called_________________?
A. absorptive power
B. emissive power
C. absorptivity
D. emissivity
E. none of the above - Depending on the radiating properties, a body will be white when_________________?
A. p = 0, x = 0 and a = 1
B. p=l,T = 0anda = 0
C. p = 0, x = 1 and a = 0
D. x = 0, a + p = 1
E. a = 0, x + p = 1.where a = absorptivity, p = reflectivity, x = transmissivity
