Consider radiation heat transfer. a) Define absorptivity, reflectivity, and transmissivity. Discuss their physicalmeanings and help your discussion with a sketch.d markel b) Explain why unity is found by adding the

three quantities defined in a) c) Define gray and diffuse surraces d) For a surface, define radiosity. Explain the physical meanings of the terms in the definition of radiosity.(3 marks) e) Consider a surface at a uniform temperature of 1000 K. Determine the maximum rate of thermal radiation that can be emitted by this surface, in Wm2 . Explain why this maximum is never obtained in reality.13 marks)