# PROBLEM 13 # 
Standard formula used 
  E_k = h*c/lambda 

 From the above it is clear that the energy corresponding to wavelength 5000 A is i.e. 2.482500 found to be less than the work function i.e. 4.8 eV . So it will not be able to liberate an electron.
 As the energy to wavelength 2000 A i.e. 6.206250 is greater than the work function. So it is sufficient to liberate electrons.