Atomic Models
Rutherford's Gold Foil Experiment · The Bohr Model of the Atom
IB Physics HL topic guide
Nuclear and Quantum Physics
Nuclear and Quantum Physics is a core part of IB Physics HL. This guide connects the syllabus ideas behind Atomic Models, Emission and Absorption Spectra, Nuclear Notation, Isotopes and Mass Defect, The Photoelectric Effect, Matter Waves and Uncertainty and 7 more units, shows how they appear in worked problems, and points you to the formulas and full lessons needed for exam revision.
What you will learn
Nuclear and Quantum Physics syllabus outline
The units below follow the structure used in the full Study to Learn course. Use the outline to identify exactly which idea needs attention, then work through the public example before continuing to the complete lesson path.
Emission and Absorption Spectra
Energy Levels and Photon Transitions · The Hydrogen Spectrum and Spectral Series
Nuclear Notation, Isotopes and Mass Defect
Nuclear Notation and Isotopes · Mass Defect and Binding Energy
The Photoelectric Effect
The Photoelectric Effect · Threshold Frequency and Intensity
Matter Waves and Uncertainty
Wave-Particle Duality and de Broglie Wavelength · Heisenberg Uncertainty Principle and Quantum Tunnelling
Types of Radioactive Decay
Alpha, Beta and Gamma Decay · Nuclear Equations and Conservation Laws · The Neutrino and Weak Interaction
The Decay Law and Half-Life
Activity and the Decay Constant · Half-Life Calculations · Radioactive Dating and Tracers
Applications and Safety
Medical Applications of Radioisotopes · Biological Effects and Safety
Nuclear Fission
Nuclear Fission and Chain Reactions · Binding Energy and Fission Energy Release
Fission Reactors and Energy
Nuclear Power Stations · Nuclear Waste and Safety
Nuclear Fusion
Nuclear Fusion and the Proton-Proton Chain · Fusion Energy from Mass Defect
Stellar Properties and Evolution
Astronomical Distances and Parallax · Stellar Properties and the H-R Diagram · The Stellar Life Cycle
Free worked preview
The Photoelectric Effect
This complete preview comes from the The Photoelectric Effect unit. It introduces the core language, shows the method in context, and gives you a real example of the lesson quality before you create an account.
Quantum Physics: Light as Particles
The photoelectric effect was the experiment that forced physicists to accept that light — which Young had proved was a wave — also behaves as a stream of particles (photons), each carrying energy . Classical wave theory cannot explain why light below a threshold frequency never ejects electrons, no matter how bright, nor why emission is instantaneous. Einstein's explanation, for which he won the Nobel Prize, introduced the photon model you will now use throughout quantum physics. After this lesson you will apply to calculate whether photoemission occurs for a given metal and light frequency, and explain why intensity controls the number of emitted electrons, not their energy.
The photoelectric effect — electrons ejected from a metal surface when light shines on it — cannot be explained by wave theory alone. Einstein explained it using photons: light delivers energy in discrete quanta.
where
energy carried by one photon (J or eV)
Planck's constant = 6.63×10⁻³⁴ J s
frequency of the light (Hz) — higher frequency = more energetic photons
Einstein's Photoelectric Equation
Each photon gives all its energy to a single electron. Some energy is used to escape the metal surface; the rest becomes kinetic energy:
where
energy of the incoming photon (J or eV)
work function of the metal (J or eV) — the minimum energy an electron needs to escape the surface; different for each metal
maximum kinetic energy of the ejected photoelectrons (J or eV) — electrons deeper in the metal escape with less energy, so this is the maximum
Use when: calculating whether emission occurs (hf must exceed Φ), finding the maximum KE of emitted electrons, or finding the stopping voltage Vs = Ek,max/e.
Worked Example — Photoelectric Effect
UV light of wavelength 200 nm is incident on a sodium surface (work function Φ = 2.28 eV). Find: (a) the photon energy in eV, (b) the maximum KE of emitted electrons, and (c) the stopping voltage.
(a) E = hc/λ = (6.63×10⁻³⁴ × 3.00×10⁸)/(200×10⁻⁹) = 9.95×10⁻¹⁹ J
E = 9.95×10⁻¹⁹ / 1.60×10⁻¹⁹ = 6.22 eV
(b) E_k,max = hf − Φ = 6.22 − 2.28 = 3.94 eV = 6.30×10⁻¹⁹ J
(c) V_s = E_k,max/e = 3.94 eV / e = 3.94 V
(a) E = hc/λ = (6.63×10⁻³⁴ × 3.00×10⁸)/(200×10⁻⁹) = 9.95×10⁻¹⁹ J
E = 9.95×10⁻¹⁹ / 1.60×10⁻¹⁹ = 6.22 eV
(b) E_k,max = hf − Φ = 6.22 − 2.28 = 3.94 eV = 6.30×10⁻¹⁹ J
(c) V_s = E_k,max/e = 3.94 eV / e = 3.94 V
Key Observations Explained
• Below the threshold frequency f₀ (where hf₀=Φ), no electrons are emitted regardless of intensity
• Increasing intensity increases the number of photoelectrons, not their maximum energy
• Emission is instantaneous — no time delay even at low intensity
• Increasing intensity increases the number of photoelectrons, not their maximum energy
• Emission is instantaneous — no time delay even at low intensity
Stopping Voltage
The stopping voltage Vs is the reverse potential needed to stop even the fastest photoelectrons.
Reviewed by the Study to Learn editorial team · Updated 2026-07-24