A block having some emissivity is maintained at 500 K temperature in a surrounding of300 K temperature. It isobserved that, to maintain the temperature of the block, 210 W external power is required to be supplied to it. If instead ofthis block a black body ofsame geometry and size is used, 700 W external power is needed for the same. Find the emissivity of the material ofthe block.

Explanation

To find the emissivity of the block, we can use Stefan-Boltzmann's law, which relates the power radiated by a body to its temperature and emissivity. The formula for power loss due to radiation is given by:

\[ P = \sigma \cdot e \cdot A \cdot (T^4 - T_s^4) \]

Where:
- \( P \) is the power radiated,
...