A large body of lava from a volcano has stopped flowing and is slowing cooling. The interior of the lava is at 1250C , its surface is at 470C , and the surroundings are at 29C.

(a) Calculate the rate at which energy is transferred by radiation from 1.3m^2 of surface lava into the surroundings, assuming the emissivity is 1.0 . Express your answer in watts.

(b) Suppose heat conduction to the surface occurs at the same rate. What is the thickness (in m) of the lava between the surface and the interior, assuming that the lava's conductivity is the same as that of brick (0.84 J/s m C)? Express your answer with two significant figures.