When ultraviolet light of wavelength 2.54*10-5 cm and intensity 0.5 mW/cm2 form a mercury arc falls upon a clean copper surface, the stopping potential necessary to stop the emission of the photo-electrons is 0.59 V.
a) What would be the stopping potential if the intensity was increased to 1.0 mW/cm2 ?
b) What would be the threshold wavelength for copper?