Modern Physics Review for AP Physics 2

Overview

• Modern physics is primarily conceptual due to advanced topics.
• Key topics include atomic structure, quantum states, and various phenomena related to energy and light.

Atomic Structure and Quantum State

• Atoms consist of a nucleus (protons and neutrons) and orbiting electrons.
• Periodic Table: Number of protons determines an element's properties.
• Isotopes: Atoms with different numbers of neutrons.
• Mass Number: Total protons + neutrons.
• Strong Nuclear Force: Binds protons and neutrons, stronger than electrostatic force.
• Bohr Model: Electrons orbit nucleus like planets, a classical model not entirely accurate.
• Quantum Model: Electrons exist in discrete energy states, known as quantum states.
  • Electrons absorb photons to move to higher energy states.
  • Release photons to move to lower energy states.

Photons and Energy

• Photons are light particles containing energy.
• Binding Energy: Energy needed for electron to escape an atom.
• Energy Conversion: Energy often measured in joules or electron volts; E=MC² relates mass and energy.
• Mass Defect: Mass lost in nuclear reactions, e.g., in nuclear fusion.

Light and Photons

• Photons: Have wave properties, energy given by HF (H is Planck's constant, F is frequency).
• De Broglie's Wavelength: Calculated using momentum.
• Photoelectric Effect: Demonstrates light consists of photons; requires specific frequency to eject electrons.
  • Kinetic energy of ejected electrons depends on photon energy minus work function.

Compton Scattering

• Interaction between photons and free electrons.
• Momentum and energy transferred results in change in photon's energy and wavelength.
• Conservation Laws: Photon loses energy, reducing frequency and increasing wavelength.

Black Body Radiation

• Warm matter emits electromagnetic energy.
• Higher Temperature: Results in higher frequency and smaller wavelength emissions.
• Emission Power: Depends on surface area, temperature (to the fourth power).

Nuclear Decay

• Involves strong nuclear force interactions.
• Alpha Decay: Emission of a helium nucleus (2 protons, 2 neutrons).
• Beta Decay:
  • Beta Positive: Proton converts to neutron, emits positron.
  • Beta Negative: Neutron converts to proton, emits electron.
• Gamma Decay: Release of energy when electrons change states.
• Conservation: Momentum, energy, mass, and charge are conserved.
• Random Process: Described by decay constant and half-life, N = N0e^(-λt).

Example Problems

• Application in multiple-choice and free-response questions.
• Radioactive Decay: Relationships between remaining nuclei and time.
• Work Function and Stopping Distance: Explained using kinetic energy principles.
• Compton Scattering: Qualitative understanding of energy changes with angle.
• Nuclear Reactions: Identification and description of decay processes.

These notes summarize the key concepts of modern physics necessary for understanding and problem-solving in AP Physics 2. They focus on atomic structures, quantum states, interactions of light and matter, and nuclear decay, providing foundational knowledge for more complex applications.