The work- function of a substance is 4.0 eV. The longest wavelength of light that can cause photoelectron emission from this substance is approximately ?: (1) 540 nm (2) 400 nm (3) 220 nm (4) 310 nm
1 Answer
310 nm.
Explanation:
Since the photon energy is inversely related to its correspondent light wavelength, the longest wavelength will be the one that leaves the photon on a threshold situation regarding its energy to free the photoelectron from the metal. Ideally, this would happen when the photon's energy equals the substance's work-function.
Then, we must have
Moreover, the photon's energy can be written as
Using
then: