← Physics 2 syllabus

United StatesPhysics 2

Unit 15: Modern Physics

5 dot points across 5 inquiry questions. Click any dot point for a focused answer with worked past exam questions where available.

Why does a hot object glow, and why does its color shift from red to white as it heats up?

Topic 15.4 Blackbody Radiation: describe the thermal radiation spectrum of a hot object and how its peak shifts with temperature.
A focused answer to AP Physics 2 Topic 15.4, covering thermal radiation from hot objects, the continuous blackbody spectrum, the shift of the peak wavelength to shorter wavelengths as temperature rises, the rise in total radiated power, and the role of quantisation in explaining the spectrum, with full worked examples.
10 min answer →

How do unstable nuclei decay, and where does the huge energy of fission and fusion come from?

Topic 15.7 Nuclear Physics and Radioactivity: describe alpha, beta and gamma decay, half-life, and the energy of fission and fusion through mass-energy equivalence.
A focused answer to AP Physics 2 Topics 15.7 and 15.8, covering the three types of radioactive decay (alpha, beta, gamma), the conservation of charge and nucleon number in nuclear equations, half-life and exponential decay, and the energy released in fission and fusion through E = mc squared, with full worked examples.
12 min answer →

How can light behave as both a wave and a stream of particles?

Topic 15.1 Quantum Theory and Wave-Particle Duality: relate photon energy to frequency and describe the wave-particle duality of light and matter.
A focused answer to AP Physics 2 Topic 15.1, covering the quantisation of light into photons, the photon energy E = hf, the wave-particle duality of light, the de Broglie wavelength of matter, and the evidence for quantum behavior, with full worked examples.
11 min answer →

Why do atoms emit and absorb light at only specific wavelengths?

Topic 15.2 The Bohr Model and Atomic Spectra: relate quantised energy levels to the emission and absorption spectra of atoms.
A focused answer to AP Physics 2 Topics 15.2 and 15.3, covering the Bohr model of quantised electron energy levels, the emission of a photon when an electron drops between levels, the relation E = hf for the photon energy, and the line emission and absorption spectra that result, with full worked examples.
11 min answer →

What experiments prove that light delivers its energy and momentum as particles?

Topic 15.5 The Photoelectric Effect and Compton Scattering: apply the photoelectric equation and describe Compton scattering as evidence of the photon.
A focused answer to AP Physics 2 Topics 15.5 and 15.6, covering the photoelectric effect, the work function and threshold frequency, the photoelectric equation Kmax = hf - phi, why the effect proves the photon model, and Compton scattering as evidence that photons carry momentum, with full worked examples.
12 min answer →