A thick walled, hollow metallic cylinder has height $h$ and inner and outer radii $r_1$ and $r_2$, respectively. It contains water which is heated with a constant power source so that its temperature is maintained at $T_1$. In the steady state, the temperature of the inner and outer isothermal surfaces of the cylinder are $T_1$ and $T_2$, respectively. The temperature difference $\left(T_1-T_2\right)$ is proportional to

• A

  $\frac{r_2-r_1}{h\left(r_2+r_1\right)}$
• Correct answer
  B

  $\frac{\ln \left(r_2 / r_1\right)}{h}$
• C

  $\frac{r_2-r_1}{h r_2} \ln \left(r_2 / r_1\right)$
• D

  $\frac{r_2-r_1}{r_2 r_1}$

Hence, the correct answer is option: 'B'.