The K_max of the emitted photoelectron is related to the stopping potential V₀ by

1. Photocurrent vanishes when the retarding potential exactly stops the fastest photoelectrons. 2. The energy needed to stop an electron of charge e across potential V₀ is eV₀. 3. Therefore K_max = eV₀ from energy conservation. 4. This is the standard formula relating stopping potential to maximum kinetic energy. _Source: syllabus Physics, Ch 11 "Dual Nature of Radiation and Matter", §11.4.2_