A photoelectric cell has a strontium cathode of work function eV
PHYSICS · Multi-part · Fermi University Physics · Optics & Photonics · Quantum Mechanics · Origins of quantum theory
Quantum Mechanics: From the Photon to the Hydrogen Atom, Ch Light in lumps: blackbody radiation, the photoelectric effect and Compton scattering
Problem
A photoelectric cell has a strontium cathode of work function W=2.59 eV. It is illuminated with monochromatic ultraviolet light of wavelength 365 nm. The cell is in vacuum, the cathode surface is clean and uniform, and photoelectrons lose no energy in collisions on the way to the anode. Take each arriving photon to have the same chance of freeing an electron at both intensities, with no heating of the cathode. Use hc=1240 eV nm.
((a)) Find the stopping potential of the cell.
((b)) The lamp is now replaced by one of the same wavelength but twice the intensity, so twice the power falls on the cathode. Find the stopping potential now.
((c)) By what factor does the number of photoelectrons leaving the cathode each second change when the intensity is doubled?