The stopping potential in a photoelectric effect setup refers to the minimum potential (voltage) required to prevent electrons from reaching the photocell after being emitted by the incident light.
If the distance between the source of light and the photocell is increased while keeping other factors constant, such as the intensity of light and the characteristics of the photocell, the stopping potential will not change. The stopping potential depends on the energy of the incident photons, which is determined by the frequency (or equivalently, the color) of the light. It is independent of the distance between the source and the photocell.
In the photoelectric effect, the energy of the incident photons determines the kinetic energy of the emitted electrons. If the frequency of the light is below a certain threshold (known as the threshold frequency), no electrons will be emitted regardless of the intensity or the distance between the source and the photocell. If the frequency exceeds the threshold, increasing the intensity of the light would result in more electrons being emitted, but it would not affect the stopping potential required to halt those electrons.
Therefore, changing the distance between the source of light and the photocell will not have any direct impact on the stopping potential in the photoelectric effect.