Quantum Physics Lecture Notes

Introduction

Builds on previous knowledge from waves and particle physics.
Models used in physics: Particle model (electrons, circuits, chemistry) and Wave model (light behavior like refraction and reflection).

Observed when light energizes the surface of materials (e.g., metals).
Wave model limitation: Does not explain how electrons leave at certain frequencies.
Particle model: Light as a packet of energy (photon).
Photon energy: Proportional to frequency (E = hf), where h is a constant.
- Higher frequency = Higher energy (e.g., blue light).
- X-rays and gamma rays are more energetic and ionizing than microwaves and radio waves.
Photoelectric Effect: Photon interacts with electron, energy must overcome material's work function for electron to escape.
- Extra energy = kinetic energy of photoelectron.

Electrons exist at different energy levels within an atom.
Absorption of energy: Electron moves up an energy level.
Emission of energy: Electron drops down, emitting a photon.
- Larger drop = More energy (E = hf) = Different color (frequency) photon.
Spectra: Emission and Absorption
- Emission spectra: Specific colors of light emitted by an element.
- Absorption spectra: Specific colors of light absorbed by an element (related to red shift in starlight).

Neither wave model nor particle model alone is sufficient.
Combination of both models: Dual nature
- Light: Exhibits wave-like (refraction, diffraction) and particle-like behavior (photoelectric effect).
- Electrons: Typically particles but also exhibit wave-like behavior (e.g., diffraction).
- Wavelength of electron: λ = h/p (momentum).

Electrons set up standing waves in atoms, explaining distinct energy levels.
Advanced quantum physics phenomena: Quantum tunneling, quantum locking, etc.
Quantum physics is often introduced in the first year of A-level after studying waves.
- Key topics: Photoelectric effect, electron energy levels, wave-particle duality.