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Modern Physics

Table of contents

Elementary particles

Nuclear physics and radioactivity

Half life of radioactive isotopes

Early quantum theory

Quantum mechanics

Einstein’s theory of special relativity

Einstein’s theory of general relativity

Astrophysics and cosmology

Unification of forces


AP Physics topics: table of contents

Big bang details, incl. nucleosynthesis

Nuclear energy

Molecules and solids


Classical physics is concerned with everyday conditions: speeds much lower than the speed of light, and sizes much greater than that of atoms. The classical laws of physics are “true”, in that they provide an immensely accurate picture of our universe works.

However, when we study particles at sub-atomic size scales,  the laws of classical mechanics completely fail; they would not allow us to build a description of atoms in any realistic way.  At the same time, as physicists began to study the motion of objects moving at very high speeds, we discovered that the ways which we measured time and space didn’t work correctly.

When James Clerk published his “A Dynamical Theory of the Electromagnetic Field “in 1865, it was discovered that light itself always moved at a constant velocity, 299,792,458 metres per second (≈3.00×108 m/s) , and that light always had this speed, no matter what one’s frame of reference was. This paradox eventually led Albert, some years later (1905) to discover his Special Theory of Relativity.

Why is “c” used to represent the speed of light

Finally, when physicists studied gravity, they found that even light itself could be attracted by gravity, forcing us to fundamentally reconceptualize what gravity actually is,

How is possible that the laws of nature appear different for most things in our ordinary, everyday world, while the laws appear completely different for the quantum and relativistic worlds? After all, we all live in the same universe. By definition there is only one truth, one ultimate set of laws.

The resolution to this seeming paradox comes when we mathematically analyze the equations of modern physics: When we look at large objects (greater than the size of a molecule) and slower speeds (less than 1% of the speed of light) we see that the modern physics equations yield approximations that are the same as our classical laws of physics.

In other words, classical physics is a special case of modern physics.

Lectures from Astronomy 123: Galaxies and the Expanding Universe

Week 01:
  1. Ancient Cosmology
  2. Medieval Cosmology
Week 02:
  1. Newtonian Cosmology
  2. Atomic Theory
  3. Clockwork Universe
Week 03:
  1. Quantum Physics
  2. Elementary Particles
  3. Relativity

Jan 31st: Exam #1

Week 04:
  1. Mass/Energy Equivalence
Week 05:
  1. Milky Way
  2. Hubble Sequence
  3. Quasars
  4. Distance Scale

External resources

JS Cosmology Course, Univ. Oregon


The Physics arXiv blog

Learning Standards

2016 Massachusetts Science and Technology/Engineering Curriculum Framework

HS-ESS1-2. Describe the astronomical evidence for the Big Bang theory, including the red shift of light from the motion of distant galaxies as an indication that the universe is currently expanding, the cosmic microwave background as the remnant radiation from the Big Bang, and the observed composition of ordinary matter of the universe, primarily found in stars and interstellar gases, which matches that predicted by the Big Bang theory (3/4 hydrogen and 1/4 helium).

SAT Subject Test: Physics

Quantum phenomena, such as photons and photoelectric effect
Atomic, such as the Rutherford and Bohr models, atomic energy levels, and atomic spectra
Nuclear and particle physics, such as radioactivity, nuclear reactions, and fundamental particles
Relativity, such as time dilation, length contraction, and mass-energy equivalence

A Framework for K-12 Science Education: Practices, Crosscutting Concepts, and Core Ideas (2012)

Electromagnetic radiation can be modeled as a wave of changing electric and magnetic fields or as particles called photons. The wave model is useful for explaining many features of electromagnetic radiation, and the particle model explains other features. Quantum theory relates the two models…. Knowledge of quantum physics enabled the development of semiconductors, computer chips, and lasers, all of which are now essential components of modern imaging, communications, and information technologies.

Massachusetts Science and Technology/Engineering Curriculum Framework 2006

Chemistry: Atomic Structure and Nuclear Chemistry
Atomic models are used to explain atoms and help us understand the interaction of elements and compounds observed on a macroscopic scale. Nuclear chemistry deals with radioactivity, nuclear processes, and nuclear properties. Nuclear reactions produce tremendous amounts of energy and lead to the formation of elements.

2.1 Recognize discoveries from Dalton (atomic theory), Thomson (the electron), Rutherford (the nucleus), and Bohr (planetary model of atom), and understand how each discovery leads to modern theory.
2.2 Describe Rutherford’s “gold foil” experiment that led to the discovery of the nuclear atom. Identify the major components (protons, neutrons, and electrons) of the nuclear atom and explain how they interact.
2.3 Interpret and apply the laws of conservation of mass, constant composition (definite proportions), and multiple proportions.
2.4 Write the electron configurations for the first twenty elements of the periodic table.
2.5 Identify the three main types of radioactive decay (alpha, beta, and gamma) and compare their properties (composition, mass, charge, and penetrating power).
2.6 Describe the process of radioactive decay by using nuclear equations, and explain the concept of half-life for an isotope (for example, C-14 is a powerful tool in determining the age of objects).
2.7 Compare and contrast nuclear fission and nuclear fusion.

AP Physics Curriculum Framework
Essential Knowledge 1.D.1: Objects classically thought of as particles can exhibit properties of waves.
a. This wavelike behavior of particles has been observed, e.g., in a double-slit experiment using elementary particles.
b. The classical models of objects do not describe their wave nature. These models break down when observing objects in small dimensions.

Learning Objective 1.D.1.1:
The student is able to explain why classical mechanics cannot describe all properties of objects by articulating the reasons that classical mechanics must be refined and an alternative explanation developed when classical particles display wave properties.

Essential Knowledge 1.D.2: Certain phenomena classically thought of as waves can exhibit properties of particles.
a. The classical models of waves do not describe the nature of a photon.
b. Momentum and energy of a photon can be related to its frequency and wavelength.

Content Connection: This essential knowledge does not produce a specific learning objective but serves as a foundation for other learning objectives in the course.


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