The peak emission from a black body at a certain temprature occurs at a wavelength of `9000 Å`. On increase its temperature , the total radiation emmited is increased its `81` times. At the intial temperature when the peak radiation from the black body is incident on a metal surface , it does not cause any photoemission from the surface . After the increase of temperature, the peak from the black body caused photoemission. To bring these photoelectrons to rest , a potential equivalent to the excitation energy between `n = 2 and n = 3` bohr levels of hydrogen atoms is required. Find the work function of the metal.