ASNT Industrial Radiography Radiation Safety Practice Test

What is the approximate mass of an electron compared to that of a proton?

1. Equal

2. About 1/1840

3. About 1/2

4. About the same

The correct answer is: About 1/1840

The mass of an electron is indeed approximately 1/1840 that of a proton, making this the correct answer. To put it into perspective, a proton has a mass of about 1.67 x 10^-27 kilograms, while an electron's mass is about 9.11 x 10^-31 kilograms. This significant difference in mass is crucial in understanding the structure of atoms, where protons and neutrons reside in the nucleus and contribute most of the atom's mass, while electrons exist in a cloud around the nucleus. In terms of significance, the much lighter mass of electrons compared to protons allows them to participate in chemical reactions and bond formation while contributing negligibly to the overall mass of the atom. The ratio of an electron's mass to a proton's mass being approximately 1/1840 reflects this dramatic difference, underscoring the electron's role in atomic structure and chemical behavior.