Final answer:
Correct option: B: the number of electrons emitted is a quarter of the initial number.
The number of electrons emitted by the photoelectric cell will be a quarter of the initial number when the light source is moved from 1m to 2m, while the energy per emitted electron remains constant.
Step-by-step explanation:
The photoelectric effect illustrates how light can cause electrons to be emitted from a metal surface. When the source of light is moved from 1m to 2m away, the intensity of light and therefore the number of photons incident on the metal surface will decrease as per the inverse square law of light intensity.
This change in distance means that the light's intensity falls to a quarter of its original intensity because intensity is inversely proportional to the square of the distance from the light source. As a result, the number of photons hitting the surface also drops to a quarter, directly reducing the number of electrons emitted by that factor. However, the energy of the individual emitted electrons does not change because it is dependent on the frequency of the light, not its intensity.
The correct answer to the question is B: the number of electrons emitted is a quarter of the initial number. This is assuming that the frequency of the light remains constant and above the threshold frequency for the photoelectric effect to occur in the photoelectric cell. The energy per each emitted electron remains the same; only the quantity of photoelectrons changes.