Stopping potential is Kmax = evo and doesn't depend on distance so option d is correct.

The photoelectric effect is a phenomenon in which electrons are emitted from a material when it is exposed to light. This effect can be explained using the concept of photons, which are particles of light that carry energy. When a photon strikes a metal surface, it transfers its energy to an electron in the metal, causing the electron to be ejected from the surface.

The stopping potential is the minimum potential difference that must be applied across a photocell to prevent the emission of electrons. It is a measure of the maximum kinetic energy of the emitted electrons. The stopping potential depends on the energy of the incident photons and the work function of the metal, which is the minimum energy required to remove an electron from the metal surface.

When a point source of light is used in the photoelectric effect and is removed farther from the emitting metal, the stopping potential remains constant. This can be explained by considering the energy of the incident photons and the work function of the metal.

- Energy of incident photons:
- The energy of a photon is directly proportional to its frequency and inversely proportional to its wavelength. As the source is moved farther from the metal, the intensity of the light decreases, but the frequency and energy of each individual photon remain constant.
- Therefore, the energy of the incident photons does not change when the source is moved farther.

- Work function of the metal:
- The work function of a metal is the minimum energy required to remove an electron from its surface. It is a characteristic property of the metal and does not change with the distance of the light source.
- Therefore, the work function of the metal remains constant when the source is moved farther.

Since both the energy of the incident photons and the work function of the metal remain constant, the stopping potential, which depends on these two factors, also remains constant. Thus, the correct answer is option 'D' - the stopping potential will remain constant when the source is removed farther from the emitting metal in the photoelectric effect.