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

Related Mcqs:

1. 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

2. 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

3. The value of the wavelength for maximum emissive power is given by ___________________?

   A. Wien’s law
   B. Planck’s law
   C. Stefan’s law
   D. Fourier’s law
   E. Kirchhoff’s law

4. The emissive power of a body depends upon its___________________?

   A. temperature
   B. wave length
   C. physical nature
   D. all of the above
   E. none of the above

5. 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

6. Two balls of same material and finish have their diameters in the ratio of 2 : 1 and both are heated to same temperature and allowed to cool by radiation. Rate of cooling by big ball as compared to smaller one will be in the ratio of____________________?

   A. 1 :1
   B. 2: 1
   C. 1 : 2
   D. 4 : 1
   E. 1 : 4

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. 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

9. The ratio of heat flow Q1/Q2 from two walls of same thickness having their thermal conductivities as ATj – 2K2 will be ________________?

   A. I
   B. 0.5
   C. 2
   D. 0.25
   E. 4.0

10. 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