A. The cooling rate will be the same for the two spheres and hence the two spheres will have
equal temperatures at any instant
B. Both the spheres will emit equal amount of radiation per unit time in the beginning
C. Both will absorb equal amount of radiation from the surrounding in the beginning
D. Both B. & C.
Related Mcqs:
- A sphere of radius ‘R1’ is enclosed in a sphere of radius ‘R2’. The view (or shape) factor for radiative heat transfer of the outer sphere with respect to the inner sphere is ________________?
A. 0
B. R2/(R1+R2)
C. 1
D. (R1/R2)2 - Three solid objects of the same material and of equal mass-a sphere, a cylinder (length = diameter) and a cube are at 500°C initially. These are dropped in a quenching bath containing a large volume of cooling oil each attaining the bath temperature eventually. The time required for 90% change in temperature is the smallest for_________________?
A. Cube
B. Cylinder
C. Sphere
D. Equal for all the three - A steel sphere of radius 0.1 m at 400°K is immersed in an oil at 300°K. If the centre of the sphere reaches 350°K in 20 minutes, how long will it take for a 0.05 m radius steel sphere to reach the same temperature (at the centre) under identical conditions? Assume that the conductive heat transfer co-efficient is infinitely large ?
A. 5 minutes
B. 10 minutes
C. 20 minutes
D. 40 minutes - 200 kg of solids (on dry basis) is subjected to a drying process for a period of 5000 seconds. The drying occurs in the constant rate period with the drying rate as, Nc = 0.5 × 10-3 kg/m2.s. The initial moisture content of the solid is 0.2 kg moisture/kg dry solid. The interfacial area available for drying is 4 m2/1000 kg of dry solid. The moisture content at the end of the drying period is (in kg moisture/kg dry solid)?
A. 0.5
B. 0.05
C. 0.1
D. 0.15 - A cube, sphere & a thin circular plate (all having same mass and made of same material) are all heated to 300°C and allowed to cool in natural air. Which one will cool the slowest ?
A. Cube
B. Plate
C. Sphere
D. All will cool at the same rate - In case of _______________ boiling, the liquid temperature is below the saturation temperature and the boiling takes place in the vicinity of the heated surface?
A. Nucleate
B. Local
C. Pool
D. Saturated - In a laboratory test run, the rate of drying was found to be 0.5 x 10-3 kg/m2.s, when the moisture content reduced from 0.4 to 0.1 on dry basis. The critical moisture content of the material is 0.08 on a dry basis. A tray dryer is used to dry 100 kg (dry basis) of the same material under identical conditions. The surface area of the material is 0.04 m2/kg of dry solid. The time required (in seconds) to reduce the moisture content of the solids from 0.3 to 0.2 (dry basis) is______________________?
A. 2000
B. 4000
C. 5000
D. 6000 - In case of heat transfer by conduction in a hollow cylinder, ______________ mean area is used to calculate the heat transfer rate?
A. Geometric
B. Arithmetic
C. Logarithmic
D. Either A., B. or C. - A wall has two layers of materials A and B; each made of a different material. Both the layers have the same thickness. The thermal conductivity of material A is twice that of B. Under the equilibrium, the temperature difference across the wall is 36°C. The temperature difference across the layer A is ______________ °C?
A. 6
B. 12
C. 18
D. 24 - A composite flat wall of a furnace is made of two materials ‘A’ and ‘B’. The thermal conductivity of ‘A’ is twice of that of material ‘B’, while the thickness of layer of ‘A’ is half that of B. If the temperature at the two sides of the wall are 400 and 1200°K, then the temperature drop (in °K) across the layer of material ‘A’ is________________?
A. 125
B. 133
C. 150
D. 160
