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Lesson 11.7 • Competency 11.7Complete Lesson
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Fundamental Particles and Interactions

The Standard Model of particle physics: Quarks (u, d, c, s, t, b), fractional charges, Leptons (e, μ, τ and neutrinos), Gauge Bosons (photon, gluon, W/Z), Hadrons (Baryons and Mesons), and the four fundamental forces of nature.

Marking a lesson complete represents finishing your study of the topic; it does not denote tested mastery.

Learning Objectives

  • Classify subatomic particles into quarks, leptons, hadrons (baryons and mesons), and gauge bosons under the Standard Model.
  • Determine quark composition of protons (uud) and neutrons (udd) and compare relative strengths and ranges of the four fundamental interactions.

Core Theory & Concepts

All observable matter in the Universe is assembled from twelve fundamental spin-1/2 fermions (six quarks and six leptons), interacting through gauge bosons representing the four fundamental physical forces.

Quarks & Nucleon Composition

Quarks possess fractional electric charges: Up (u) = +2/3 e, Down (d) = -1/3 e. A proton is a baryon formed from (u + u + d): net charge = 2/3 + 2/3 - 1/3 = +1 e. A neutron is formed from (u + d + d): net charge = 2/3 - 1/3 - 1/3 = 0.

p = (uud) \implies +1 e, \quad n = (udd) \implies 0 e

The Four Fundamental Forces

1. Strong Nuclear Force (relative strength 1, range ≈ 10⁻¹⁵ m, mediated by gluons). 2. Electromagnetic Force (relative strength 10⁻², range infinite, mediated by photons). 3. Weak Nuclear Force (relative strength 10⁻⁶, range ≈ 10⁻¹⁸ m, mediated by W±, Z⁰ bosons; causes beta decay). 4. Gravitational Force (relative strength 10⁻³⁹, range infinite, mediated by graviton).

Common Misconceptions

Misconception

Electrons are composed of quarks just like protons and neutrons.

Physical Clarification:Electrons are fundamental LEPTONS with zero substructure. They do not experience the strong nuclear force and are NOT made of quarks.

Syllabus Topic Outline

Competency 11.7
  • 1Structure of matter: atoms → nuclei → nucleons → elementary quarks
  • 2The Six Quark flavors: Up (+2/3e), Down (-1/3e), Charm (+2/3e), Strange (-1/3e), Top (+2/3e), Bottom (-1/3e)
  • 3Hadrons: Baryons (qqq: proton = uud, neutron = udd) and Mesons (q q̄: pions)
  • 4Leptons (do not feel strong force): electron, muon, tau, and corresponding neutrinos
  • 5Four fundamental interactions: Strong (gluon), Electromagnetic (photon), Weak (W±, Z⁰), Gravitational (graviton)
  • 6Conservation laws: charge, baryon number, and lepton number in nuclear decays

Practice Problems