The beam Chadwick observed was not affected by magnets or charged objects. This indicated what about the particles?

• A. They were light particles
• B. They were neutral particles
• C. They were electrons
• D. They were protons

Answer: (B)

The key idea is that electromagnetic fields only push or bend things that carry electric charge. In a magnetic field, a moving charged particle experiences a force proportional to its charge (the Lorentz force). If a beam isn’t deflected by magnets or by other charged objects, the particles must have no net electric charge. That’s why this observation points to neutral particles. Chadwick’s finding was that the neutron—a neutral particle with mass—exists. Charged particles like electrons or protons would be deflected, regardless of their mass, so the lack of deflection rules out them being charged. A neutral particle can have mass and still move straight through magnetic fields because there’s no electromagnetic interaction to bend its path.