Unit 15
Modern physics.
What classical physics could not explain: the atom, radioactivity, photons, matter waves and relativity.
Before this unit
- Light and optics
- Exponents and logarithms Mathematics
The unit, lesson by lesson
Lessons
7 lessons · 36 practice questions · about 3 hours
Atoms and nuclei
What an atom is made of: protons and neutrons in a tiny nucleus with electrons around it, the atomic number and the mass number, isotopes, electron shells, and why an electron is not a planet.
Radioactive decay
What comes out of an unstable nucleus and what is left of it: alpha decay, beta decay and gamma rays, nuclear equations, a nucleus with no memory, and the activity of a radioactive source.
Photons
The photoelectric effect: a threshold frequency that brightness cannot get past, the energy of a photon, the work function, the stopping voltage, and the speed of the fastest electron.
Matter waves
Single electrons that build an interference pattern: the de Broglie wavelength, how the gun voltage sets it, what happens when you check which slit each electron went through, and what this wave really is.
Quantum tunnelling
An electron can be found past a wall higher than its energy: the wave fading inside the wall, the depth at which the chance halves, a slightly thicker or higher wall letting far less through, and energy kept on the far side.
Special relativity
A light clock on a fast train: the speed of light is the same for every observer, the Lorentz factor from Pythagoras, time dilation, length contraction, and muons that reach the ground.
Superconductivity
Below its critical temperature a material's resistance vanishes completely, and it keeps magnetic fields out: the Meissner effect, a floating magnet, why cold copper does not do it, and why YBCO and liquid nitrogen changed the picture.