If the inner and oute r surfaces of a hollow cylinder (having radii $$r_1 and r_2$$ and length L) are at temperatures $$t_1 and t_2$$ then rate of radial heat flow will be

A

$$\frac {k}{2\pi L} \frac {t_1 -t_2}{\log \frac{r_2}{r_2}}$$

B

$$\frac {1}{2\pi Lk} \frac {t_1 -t_2}{\log \frac{r_2}{r_1}}$$

C

$$\frac {2\pi L}{k} \frac {t_1 -t_2}{\log \frac{r_2}{r_1}}$$

D

$$2 \pi Lk \frac {t_1 -t_2}{\log \frac{r_2}{r_1}}$$