question_answer

The figure shows a system of two concentric spheres of radii \[{{\operatorname{r}}_{1}}\]and \[{{r}_{2}}\] are kept at temperatures \[{{T}_{1}}\] and \[{{T}_{2}}\]respectively. The radial rate of flow of heat in a substance between the two concentric spheres is proportional to

A) \[ln\left( \frac{{{r}_{2}}}{{{r}_{1}}} \right)\]

B) \[\frac{\left( {{r}_{2}}-{{r}_{1}} \right)}{\left( {{r}_{1}}{{r}_{2}} \right)}\]

C) \[\left( {{r}_{2}}-{{r}_{1}} \right)\]

D) \[\frac{{{r}_{1}}\,{{r}_{2}}}{({{r}_{2}}-{{r}_{1}})}\]