Atomic Physics – Experiment Proving the Small Size of the Nucleus
Question:
(3 pts) Which of the following experiments showed that the atomic nucleus is very small compared to the size of the whole atom?
- a) Rutherford Backscattering
- b) Blackbody Radiation
- c) Compton Scattering
- d) Photoelectric Effect
- e) Electron Diffraction
Answer and Detailed Explanation:
✅ Correct Answer: a) Rutherford Backscattering
Rutherford’s famous gold foil experiment was a landmark test in nuclear and atomic physics. In this experiment, alpha particles (helium nuclei) were directed at a thin sheet of gold foil.
🔬 Key Observations:
- Most of the alpha particles passed straight through the foil with little or no deflection.
- A very small number were deflected at large angles.
- A few even bounced back toward the source.
💡 Interpretation:
These unexpected results led Rutherford to propose that:
- Most of the atom is empty space.
- The positive charge and most of the atom’s mass is concentrated in a very small, dense nucleus.
🚫 Why Not the Other Options?
- Blackbody Radiation — Related to quantum theory and energy quantization, not structure.
- Compton Scattering — Demonstrated photon momentum; relates to quantum particle nature of light.
- Photoelectric Effect — Shows particle nature of light; doesn’t concern atom size.
- Electron Diffraction — Demonstrates wave nature of electrons, not size of nucleus.
✅ Conclusion:
The Rutherford Backscattering Experiment provided the first evidence that the atomic nucleus is very small and dense, with the rest of the atom being mostly empty space.
The Rutherford Backscattering Experiment provided the first evidence that the atomic nucleus is very small and dense, with the rest of the atom being mostly empty space.