PHYSICS · Multi-part · Fermi University Physics · Optics & Photonics · Photodetection, photonic sources and quantum optics · Photodetection, photonic sources and quantum optics
Optics and Photonics, Ch The photon
Problem
A clean zinc plate has work function W=4.3 eV. It is illuminated by an intense red laser of wavelength 633 nm delivering a power of 10 W focused onto a spot of area 1.0 mm2 (irradiance about 107 W m−2, far brighter than the faint lamp of the accumulation-time estimate in the text). A student argues: "the classical accumulation-time estimate in this chapter showed that a weak lamp needs about two hours to deliver 4.3 eV to one atom. This laser is enormously more intense, so it must deliver enough energy per electron in well under a second, and photoelectrons should appear."
((a)) Compute the photon energy of the 633 nm light in eV.
((b)) Compare it with W and state whether photoelectrons are emitted, however intense the beam.
((c)) Explain in one or two sentences why the accumulation-time argument does not apply here, even though the beam is intense.