A thin black plate is hung on a string in a glass vacuum flask and exposed to the Sun so that the rays from the Sun fall perpendicular to the plate. The heat flux density that reaches the Earth from the Sun is 
(solar constant). What is the temperature of the plate when thermal equilibrium is established? Calculate for the following two cases:
When we ignore the influence of the Earth's atmosphere on the heat flux that reaches the Earth.
When we consider that the Earth's atmosphere reduces the heat flux density that reaches the plate to 70% of the initial value.
and 
respectively.
