The figure shows a system of two concentric spheres of radii r1 and r2 and kept at temperatures T1 and T2, respectively. The radial rate of flow of heat in a substance between the two concentric spheres is proportional to [AIEEE 2005]

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

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

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

The figure shows a system of two concentric spheres of radii r1 and r2

1.	The figure shows a system of two concentric spheres of radii r1 and r2 and kept at temperatures T1 and T2, respectively. The radial rate of flow of heat in a substance between the two concentric spheres is proportional to [AIEEE 2005]
A.	\[\frac{{{r}_{1}}\,{{r}_{2}}}{({{r}_{1}}-{{r}_{2}})}\]
B.	\[({{r}_{2}}-{{r}_{1}})\]
C.	\[({{r}_{2}}-{{r}_{1}})({{r}_{1}}\,{{r}_{2}})\]
D.	In \[\left( \frac{{{r}_{2}}}{{{r}_{1}}} \right)\]
Answer» B. \[({{r}_{2}}-{{r}_{1}})\]