The photoelectric effect is a fundamental subject taught as a part of physics courses in both high
schools and universities. It is a phenomenon relating to the ejection of electrons from a metal
surface by the action of light (or electromagnetic radiation). Some of the textbooks commonly used
in those courses contain a crucial conceptual error concerning the meaning of stopping potential in
Millikan’s arrangement of the photoelectric effect. In this paper, I point to this error, detail an
explanation of the error by explaining the actual meaning of stopping potential and offer some
experiments to clarify it.