AP Night Lecture #6:
Nuclear Physics
Online Video Lessons:
For animated lessons with narration and problems, visit HippoCampus's
- Wave and particle duality (continued)
- de Broglie postulated matter could also act like a wave with momentum p = h / λ
- Since particles can act like waves, we can never simultaneously measure a particle's position and velocity with complete accuracy (Heisenberg's Uncertainty Principle)
- Nuclear model
- Bohr proposed a model with electrons orbiting nucleus at specific energy levels; only able to jump directly from one to level to another by emitting or absorbing photons of light of corresponding frequency
- Bohr model only works for hydrogen, modern models go further and say electron appears at different positions with varying probability; the most probable locations for an electron correspond to Bohr's old "energy levels" idea; electrons thus appear in probability shells and form a type of "electron cloud"
- Radioactivity
- Alpha (α) particles: Helium nucleus 42He, so massive and easily stopped
- Beta (β) particles: Neutron decays into proton and emitted electron; electron is the beta particle or 0-1e
- Gamma (γ) rays: High-energy photons emitted from the nucleus; no nuclear particle changes; massless photons difficult to stop
- Nuclear reactions
- decay: nucleus emitting particles (e.g. α, β) and changing form
- bombardment: firing particles (e.g. α, β, neutrons) at nuclei to cause them to change
- fission: heavy atoms (e.g. uranium) splitting to form lighter atoms while losing mass, so releasing energy
- fusion: light atoms (hydrogen) combining to form heavier atoms while losing mass, so releasing energy; typically uses deuterium 21H (hydrogen atom with proton & neutron; nucleus-only called deuteron) and tritium 31H (hydrogen isotope with 2 neutrons; nucleus-only is triton)
- annihilation of matter and anti-matter (use E=mc2 to predict energy released when all matter is converted)