For given combined radiative and convective heat transfer coefficient ‘h;’ and given thermal conductivity kCritical thickness of insulation for cylinder and sphere is given as

A

$$\frac{k}{h_{1}} and \frac{k}{h_{1}^{2}}$$

B

$$\frac{k}{h_{1}} and \frac{2k}{h_{1}}$$

C

$$\frac{2k}{h_{1}} and \frac{k}{h_{1}^{2}}$$

D

$$\frac{2k}{h_{1}} and \frac{k}{h_{1}}$$