Germany Jahrgangsstufe 13 Physics

Chapters: 5

1. Basic ideas of quantum physics

Properties of quantum objects · The quantum physics worldview

Matter Waves and the de Broglie Relation – Light behaves like a wave and a particle. In 1924 Louis de Broglie said matter does the same: every moving particle has a wave with wavelength λ = h/p = h/mv. For a body of kinetic energy K, λ = h/√(2mK); for an electron accelerated through V volts, λ = 1.227/√V nm. Everyday objects have far too tiny a λ to notice, but electrons have λ about the size of atoms.
Quantum Physics Basics: Double Slit, Superposition and Measurement – Tiny things like photons and electrons are "quantum objects". Each one is detected as a single dot (like a particle), but where the dots land follows a wave of probability, which makes stripes. Before we measure, a quantum object can be in a superposition of possibilities. If we find out which path it took, the stripes disappear. Quantum computers and quantum cryptography use these rules.

A quantum model of the atom

Quantum Mechanical Model: Quantum Numbers, Orbitals and Configuration – Moving electrons also behave like waves: λ = h/mv (de Broglie). Because of this we cannot know exact position and momentum together: Δx·Δp ≥ h/4π (Heisenberg). So we drop sharp orbits and use orbitals: regions where the electron is likely to be, from the Schrödinger equation (ψ² gives probability). Four quantum numbers describe each electron: n (shell, size, energy), l (subshell, shape: 0 to n−1), mₗ (orientation: −l to +l) and mₛ (spin: +½ or −½). s is spherical, p is dumbbell, d is mostly four-lobed. Electrons fill by the Aufbau (n + l) rule, Pauli principle (max 2, opposite spins) and Hund's rule (single first). Half-filled and fully filled subshells are extra stable, so Cr is 3d⁵4s¹ and Cu is 3d¹⁰4s¹.

Probing the structure of matter

Modern Physics: Quantum Theory and Relativity – Modern physics began around 1900, when classical physics failed for the very small and the very fast. Quantum theory says energy comes in packets: a photon has E = hf. The photoelectric effect shows light acts as particles, while interference shows particles such as electrons act as waves (λ = h/p). Special relativity says the speed of light is the same for all observers, so moving clocks run slow (t = γt₀), moving lengths shrink, and mass is energy (E = mc²). These ideas power lasers, solar cells, electron microscopes, GPS and nuclear energy.

A simple model of the nucleus · Radioactivity and nuclear power

Nuclear Physics: the Nucleus and Radioactivity – The nucleus holds protons (Z) and neutrons (N); mass number A = Z + N. Isotopes have the same Z but different N. Unstable nuclei decay at random: alpha decay removes 2 protons and 2 neutrons (A − 4, Z − 2), beta-minus decay turns a neutron into a proton and an electron (Z + 1), and gamma is energy only. Half-life is the time for half the nuclei in a sample to decay.
Nuclei: Size, Nuclear Force, Binding Energy, Fission and Fusion – A nucleus is made of Z protons and N neutrons (A = Z + N nucleons). Its radius is R = R₀A^(1/3) with R₀ ≈ 1.2 fm, so every nucleus has almost the same huge density. A very strong, short-range nuclear force holds the nucleons together. The nucleus weighs a little less than its loose parts; this mass defect Δm is the binding energy, E = Δm c² (1 u = 931.5 MeV). Binding energy per nucleon is highest near iron (A ≈ 56), so heavy nuclei give energy when they split (fission) and light nuclei give energy when they join (fusion).

Physics lab experiments, year 13

The Scientific Method – The scientific method is the careful way scientists find out how the world works. Observe something, ask a testable question, make a hypothesis (a clear, testable guess), test it with a fair experiment (change one variable, measure one, keep the rest the same), repeat and record data, analyse it, draw a conclusion and share it so others can check. Results that fail the test are useful too: they send you back to a new hypothesis.