Physics › Section U · Quantum and atomic physics › Topic U.4
Discovering the atom and its parts
No one can see an atom with visible light, yet by 1911 physicists knew that atoms exist, how big they are, and that each holds tiny electrons around an even tinier nucleus. The experiments that showed it used nothing more than the electric and magnetic forces you already know.
In this topic
- An old idea, indirect evidence
- Brownian motion: the first direct evidence
- Cathode rays
- Measuring e/m
- Worked example: Thomson's ratio
- Millikan's oil drops
- Worked example: counting electrons on a drop
- Rutherford scattering
- The nuclear atom
- Worked example: how small is the nucleus?
- Common mistakes to avoid
- Key takeaways
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