Key Concepts in Physics

Constituents of the Atom

• Atoms consist of protons, neutrons, and electrons.
• Protons and neutrons (nucleons) are in the nucleus; electrons are in orbitals.
• Protons: charge +1; Electrons: charge -1.
• An isotope has the same atomic number (protons) but a different number of neutrons.

Forces in the Nucleus

• Strong nuclear force acts between nucleons at short ranges (3 fm - 0.5 fm).
• Attractive within 3fm, repulsive below 0.5fm.
• It overcomes electrostatic repulsion among protons.

Types of Decay

• Beta Minus Decay: Neutron to proton, emits an electron and an antineutrino.
• Beta Plus Decay: Proton to neutron, emits a positron and an electron neutrino.
• Alpha Decay: Helium nucleus emitted (alpha particle).

Photons

• Photon energy: $E = \frac{hc}{\lambda}$ where $h = 6.63 \times 10^{-34} ext{ J.s}$ and $c = 3 \times 10^{8} ext{ m/s}$.

Antimatter

• Antiparticles: same mass, opposite charges. Annihilation results in two photons.

Pair Production

• Energy from a photon converts into a particle-antiparticle pair when interacting with a nucleus.

Particle Interactions

• Exchange particles carry fundamental forces and influence range effectiveness:
  • Strong: Pions (affect hadrons)
  • Electromagnetic: Virtual Photon (affect charged particles)
  • Weak: W⁻/W⁺ Bosons (affect all types)
• Four interactions: weak nuclear, strong nuclear, electromagnetic, gravity.

Classification of Particles

• Hadrons (strong force, made of quarks):
  • Baryons (3 quarks, decay into protons): protons, neutrons.
  • Mesons (quark-antiquark pairs): pions, kaons.
• Leptons (do not interact via strong force): electrons, muons, neutrinos.

Quarks

• Quark Types:
  • Up (u): +2/3 charge
  • Down (d): -1/3 charge
  • Strange (s): -1/3 charge
• Quarks manifest only in groups (baryons or mesons).

Conservation in Interactions

• Conservation laws for charge, baryon number, lepton number, and strangeness are crucial for understanding particle interactions.
• Example: Strange particles contain strange quarks and are created via strong interaction but decay by weak interaction.

The Photoelectric Effect

• Electrons emitted from a metal when energy of photons exceeds threshold frequency (related to work function).
• Equation: $hf = 𝜑 + E<em>{k</em>{max}}$ (threshold frequency = $\frac{𝜑}{h}$).

Electron Energy Levels

• Electrons exist in discrete energy levels.
• Ionization removes electrons; excitation raises them to higher energy.
• Emission/absorption spectra show corresponding photon energies.

Fluorescent Tubes

• Free electrons collide with mercury, exciting electrons to emit UV which is then absorbed by phosphorous to emit visible light.

Wave-Particle Duality

• Light shows wave properties (diffraction) and particle properties (photoelectric effect).
• Electrons can display diffraction and are deflected by electric fields.