Which particle has a positive electric charge and a mass around 1 amu?

Which particle has a positive electric charge and a mass around 1 amu?

• A. Proton
• B. Neutron
• C. Electron
• D. Muon

Answer: (A)

The key idea is matching both charge and mass to identify the particle. A particle with a positive electric charge and a mass near 1 amu is the proton: it carries +1e of charge and has a mass about 1 amu (around 1.0073 u). The neutron has no charge, so it doesn’t fit. The electron is far lighter (about 1/1836 of a proton) and negatively charged, so it also doesn’t fit. The muon is charged as well, but its mass is much heavier than an electron and only about 0.11 amu, not near 1 amu. So the proton best matches both criteria.

The key idea is matching both charge and mass to identify the particle. A particle with a positive electric charge and a mass near 1 amu is the proton: it carries +1e of charge and has a mass about 1 amu (around 1.0073 u). The neutron has no charge, so it doesn’t fit. The electron is far lighter (about 1/1836 of a proton) and negatively charged, so it also doesn’t fit. The muon is charged as well, but its mass is much heavier than an electron and only about 0.11 amu, not near 1 amu. So the proton best matches both criteria.