Physics for Information Science

Why some solids conduct and others do not, answered twice: once with a classical model that gets the right number for the wrong reason, and once with the quantum picture that explains what the classical model cannot. Then superconductivity, where resistance does not merely fall but stops.

The rules change when things get small enough. Uncertainty first — stated, not derived, and then used to settle a real question about what can live inside a nucleus. Then the wave function, the equation it obeys, and the one problem you can solve completely by hand: a particle trapped in a box, where quantisation drops out of the mathematics rather than being assumed.

The module the rest of your degree stands on. Carrier densities derived rather than quoted, doping and what it does to the Fermi level, and then the p-n junction — where a single boundary between two doped regions produces a device that passes current one way and not the other, and the diode equation that says by how much.

What the junction is actually for. Rectifiers turning AC into DC and the arithmetic of how badly; two diodes that are useful precisely because they break the ordinary rules; and the optoelectronic family — laser, photodiode, solar cell, LED — where photons and carriers convert into one another in both directions.