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____________________?

Related Mcqs:

1. 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

2. According to Stefan-Boltzmann law, ideal radiators emit radiant energy at a rate proportional to___________________?

   A. absolute temperature
   B. square of temperature
   C. fourth power of absolute temperature
   D. fourth power of temperature
   E. cube of absolute temperature

3. 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

4. Total emissivity of polished silver compared to black body is___________________?

   A. same
   B. higher
   C. more or less same
   D. very much lower
   E. very much higher

5. The total emissivity power is .defined as the total amount of radiation emitted by a black body per unit_______________?

   A. temperature
   B. thickness
   C. area
   D. time
   E. area and time

6. The rate of energy emission from unit surface area through unit solid angle, along a normal to the surface, is known as ________________?

   A. emissivity
   B. transmissivity
   C. reflectivity
   D. intensity of radiation
   E. absorptivity

7. 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

8. 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

9. If the temperature of a solid surface changes form 27°C to 627°C, then its emissive power changes in the ratio of___________________?

   A. 3
   B. 6
   C. 9
   D. 27
   E. 81

10. The energy distribution of an ideal reflector at higher temperatures is largely in the range of ___________________?

    A. shorter wavelength
    B. longer wavelength
    C. remains same at all wavelengths
    D. wavelength has nothing to do with it
    E. none of the above