A diathermanous substance _______________ the thermal radiation completely?

Related Mcqs:

1. The thermal efficiency of a reversible heat engine operating between two given thermal reservoirs is 0.4. The device is used either as a refrigerator or as a heat pump between the same reservoirs. Then the coefficient of performance as a refrigerator (COP)R and the co-efficient of performance as a heat pump (COP)HP are _______________?

   A. (COP)R = (COP)HP = 0.6
   B. (COP)R = 2.5; (COP)HP = 1.5
   C. (COP)R = 1.5; (COP)HP = 2.5
   D. (COP)R = (COP)HP = 2.5

2. The thermal radiation emitted by a body is proportional to Tn, where T is its absolute temperature. The value of ‘n’ is exactly 4 for__________________?

   A. Black painted bodies only
   B. All bodies
   C. Polished bodies only
   D. A black body

3. The variation of thermal conductivity of a metal with temperature is often correlated using an expression of the form K = K0 + at, where, K is the thermal conductivity and T is the temperature (in °K). The units of ‘a’ in SI system will be________________?

   A. W/m.k
   B. W/m
   C. W/m.k2
   D. None, ‘a’ is just a number

4. For gases, the thermal conductivity increases with temperature rise. For liquids, with increase in concentration, its thermal conductivity generally ?

   A. Decreases
   B. Increases
   C. Remains unchanged
   D. Increases exponentially

5. Thermal conductivities of most of the liquids _______________ with rise in temperature?

   A. Increases
   B. Decreases
   C. Remains unchanged
   D. May increase or decrease; depends on the liquid

6. The ratio of kinematic viscosity to thermal diffusivity is called the _______________ number?

   A. Peclet
   B. Prandtl
   C. Stanton
   D. Nusselt

7. A perfect black body is a perfect _____________ of radiation?

   A. Absorber
   B. Emitter
   C. Both A. & B.
   D. Neither A. nor B.

8. Electro-magnetic spectrum range, which is important for radiation varies from _____________ microns?

   A. 1 to 100
   B. 0.5 to 50
   C. 10 to 100
   D. 100 to 1000

9. The interchange factor for radiation heat transfer from surface ‘x’ to surface ‘y’ in case of an infinite parallel planes with emissivities εx & εy is given by_______________?

   A. εx + εy
   B. εx . εy
   C. 1/εx + 1/εy
   D. (εx + εy)/( εx + εy – εx . εy)

10. A black body when hot, emits heat radiation of _____________ wavelengths?

    A. Small
    B. Large
    C. All
    D. One fixed