Indicate which of the following photons can cause emission of photoelectrons from a surface of gallium (   6.7 J).
A)350 nm
B)400 nm
C)200 nm
D)650 nm
E)500 nm

Question

Indicate which of the following photons can cause emission of photoelectrons from a surface of gallium (   6.7  J).
A)350 nm 
B)400 nm 
C)200 nm 
D)650 nm 
E)500 nm

Quizplus · Accepted Answer

The energy of a photon is given by E=hc/λ, where h is Planck's constant, c is the speed of light, and λ is the wavelength of the photon. The energy required to eject a photoelectron from a metal surface (i.e. the work function) depends on the metal. For gallium, the work function is about 4.06 eV (~200 nm). 
Thus, the photons with the shortest wavelengths (i.e. highest energy) are able to cause emission of photoelectrons from gallium. 200 nm is the shortest wavelength in the given options which falls within the range of work function of gallium.

Indicate Which of the Following Photons Can Cause Emission of Photoelectrons