P1: Particle Physics and Quantum Phenomena

Year 1 / ASYear 2 / A-Level All Boards (AQA, Edexcel, OCR, WJEC, CCEA) AQA

Quarks, leptons, fundamental forces, conservation laws, photoelectric effect, wave-particle duality, de Broglie relation.

Exam Board:

📋 Key Definitions and Core Concepts

Photoelectric Effect: Emission of electrons from metal surface when irradiated with EM radiation above threshold frequency f₀.

Work Function (Φ): Minimum photon energy required to liberate an electron from metal surface: hf₀ = Φ.

Hadrons = Baryons (3 quarks: proton uud, neutron udd) + Mesons (quark-antiquark). Leptons = fundamental (e⁻, μ⁻, τ⁻, neutrinos).
Photoelectric equation: hf = Φ + E_k(max) = hf₀ + ½mv_max².
De Broglie wavelength: λ = h / p = h / (mv).

Exam-Style Question

Question:

Light of f = 1.2 × 10¹⁵ Hz hits zinc (Φ = 4.3 eV). Find max kinetic energy in eV (h = 6.63 × 10⁻³⁴ J·s).

Model Solution & Mark Scheme:

Photon energy E = hf = (6.63 × 10⁻³⁴)(1.2 × 10¹⁵) = 7.956 × 10⁻¹⁹ J = 4.97 eV.
E_k(max) = hf - Φ = 4.97 - 4.30 = 0.67 eV (1.07 × 10⁻¹⁹ J).

Q1: State quark transformation in β⁻ decay.

Show Model Answer

Answer: Down quark changes to up quark via weak interaction: d → u + e⁻ + ν̄_e.

Q2: Calculate de Broglie wavelength of electron (m = 9.11 × 10⁻³¹ kg) accelerated through 150 V.

Show Model Answer

Answer: E_k = 1.6 × 10⁻¹⁹ × 150 = 2.4 × 10⁻¹⁷ J. p = √(2mE_k) = 6.61 × 10⁻²⁴ kg m/s => λ = h/p = 0.10 nm.

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