The heat transfer by conduction through a thick cylinder of inner radius $$r_{1}$$ ,outer radius $$r_{2}$$, Higher temperature $$T_{1}$$,lower temperature $$T_{2}$$, length of cylinder l and thermal conductivity k is given by:

A

$$ \frac{2 \pi  lk (T_{1}-T_{2})}{2.3 \log \left(\frac{r_{2}}{r_{1}}\right)}$$

B

$$\frac{2.3 \log \left(\frac{r_{2}}{r_{1}}\right)}{2 \pi lk (T_{1}-T_{2})}$$

C

$$\frac{2 \pi (T_{1}-T_{2})}{2.3  lk \log \left(\frac{r_{2}}{r_{1}}\right)}$$

D

$$ \frac{2 \pi lk}{2.3(T_{2}-T_{1}) \log \left(\frac{r_{2}}{r_{1}}\right)}$$