The photoelectric work function

Define photoelectric work function. How is it related to thresold frequency?

The threshold wavelength for a metal surface whose photoelectric work function is 3.313 eV is……………………

The threshold wavelength for a metal surface whose photoelectric work function is 3.313eV is

UV radiation of energy 4 eV falls on caesium surface whose photoelectric work function is 1.95 eV. The kinetic energy of the fastest photoelectrons is