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

Related Mcqs:

1. 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

2. Heat conducted througfi unit area and unit thick face per unit time when temperature difference between opposite faces is unity,is called__________________?

   A. thermal resistance
   B. thermal coefficient
   C. temperature gradient
   D. thermal conductivity
   E. heat-transfer

3. 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

4. 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

5. According to Wien’s law, the wavelength corresponding to maximum energy is proportion to ________________?

   A. absolute temperature (T)
   B. I2
   C. f
   D. t
   E. 1/r

6. 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

7. Thermal conductivity of solid metals with rise in temperature normally___________________?

   A. increases
   B. decreases
   C. remains constant
   D. may increase or decrease depending on temperature
   E. unpredictable

8. 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

9. In heat transfer, conductance equals conductivity (kcal/hr/sqm/°C/cm) divided by ________________?

   A. hr (time)
   B. sqm (area)
   C. °C (temperature)
   D. cm (thickness)
   E. kcal (heat).

10. Thermal conductivity of glass-wool varies from sample to sample because of variation in ________________ ?

    A. composition
    B. density
    C. porosity
    D. structure
    E. all of the above