A sphere of surface area \(4\ \text{m}^2\) at temperature \(400\ \text{K}\) and having emissivity \(0.5\) is located in an environment of temperature \(200\ \text{K}\). The net rate of energy exchange of the sphere is
\[
\text{Stefan Boltzmann constant } \sigma=5.67\times10^{-8}\ \text{W m}^{-2}\text{K}^{-4}
\]