A laser beam with adjustable wavelength & in the range of 400 m - 600 nm is incident on the cathode of a photocell.

a) When the wavelength of laser beam is adjusted to 450 nm, the shortest de Broglie wavelength of the photoelectrons emitted from the cathode is 1.22 nm. Determine the workfunction of the cathode. (Answer: 1.74eV)

b) If a negative voltage of 1.20 V is applied to the anode of the photocell, determine the wavelength range of the laser beam that will not be detected by the photocell.(answer: 421nm -600nm)