Consider a solid sphere placed in surrounding with small temperature difference between sphere's surface and surrounding. If `DeltaT` and `r` represent temperature difference (between sphere and surrounding) and radius of sphere respectively, rate of cooling of the sphere is directly proportional to:

Options

A. `(DeltaT)^(4)`
B. `DeltaT`
C. `r^(2)`
D. `1/r`

Answer

B, D

Explanation

rate of cooling `=(4esigmaADeltaT)/(ms)` if `DeltaT` is small
`=(4esigma(4pir^(2))DeltaT)/(rho34/3pir^(3)s)`