In the scenario described, the difference in the motion of the alpha particles in relation to the nuclei with 20 protons and 100 neutrons versus the nuclei with 100 protons and 20 neutrons can be attributed to the nature of the forces involved.
Alpha particles are positively charged, as they consist of 2 protons and 2 neutrons. The key point here is that protons repel each other due to electromagnetic repulsion, while neutrons do not have a charge and therefore do not exert a repulsive force on the alpha particles.
In the case of the nucleus with 20 protons and 100 neutrons:
- The alpha particles can get relatively close because there are fewer protons to repel them.
In the case of the nucleus with 100 protons and 20 neutrons:
- The alpha particles cannot get as close because the significant number of protons creates a strong repulsive force, pushing the alpha particles away.
Thus, the correct response is:
Protons repel the particles, while neutrons do not.