A thick spherical shell has an inner radius of $10\ \text{cm}$ and an outer radius of $20\ \text{cm}$, and is made of a material of thermal conductivity $0.50\ \text{W/(m K)}$, as shown in the figure. Its inner surface is kept at $100\ ^\circ\text{C}$ and its outer surface at $0\ ^\circ\text{C}$. Consider the steady state. Which of the following statements are correct?

Fig. 1: Cross-section of a thick spherical shell with inner radius 10 cm and outer radius 20 cm. The inner surface is at 100 degrees Celsius and the outer surface at 0 degrees Celsius.