A. Cube
B. Plate
C. Sphere
D. All will cool at the same rate
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 - 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 - A hollow sphere and a solid sphere of the same material and equal radii are heated to the same temperature. In this case ?
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. - A composite wall consists of two plates A and B placed in series normal to the flow of heat. The thermal conductivities are kA and kB and the specific heat capacities are CPA and CPB for plates A and B respectively. Plate B has twice the thickness of plate A. At steady state, the temperature difference across plate A is greater than that across plate B, when_________________?
A. CPA > CPB
B. CPA < CPB
C. kA < 0.5 kB
D. kA >2 kB - 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 - If average heat transfer co-efficient is ha and the local coefficient at the end of the plate is hl then in case of heat transfer to a fluid flowing over a flat plate, heated over its entire length________________?
A. ha = hl
B. ha = 2hl
C. ha = 0.5 hl
D. ha = 0.75 hl - If the thermal conductivity of a wall material is independent of temperature, the steady state temperature distribution in the very large thin plane wall having steady, uniform surface temperature follows _____________ law?
A. Parabolic
B. Hyperbolic
C. Linear
D. Logarithmic - If the thermal conductivity of a wall material is independent of temperature, the steady state temperature distribution in the very large thin plane wall having steady, uniform surface temperature follows ____________ law?
A. Hyperbolic
B. Parabolic
C. Linear
D. Logarithmic - At what value of Prandtl number, the hydrodynamic and thermal boundary layers of a fluid flowing over a heated plate will be identical ?
A. 1
B. 1
D. None of these - A metal ball of radius 0.1 m at a uniform temperature of 90°C is left in air at 30°C. The density and the specific heat of the metal are 3000 kg/m3 and 0.4 kJ/kg.K respectively. The heat transfer co-efficient is 50 W/m2.K Neglecting the temperature gradients inside the ball, the time taken (in hours) for the ball to cool to 60°C is_________________?
A. 555
B. 55.5
C. 0.55
D. 0.15
