Pick at least one — physics is a contact sport, and you will not really feel any of this until you do.
- Measure the voltage of a battery with a multimeter. Put the battery on the bench. Set a digital multimeter to DC volts, touch one probe to each terminal. Compare to the printed rating. Now stick a 100 Ω resistor across the battery (briefly!) and measure the voltage again — it will sag slightly because of the battery's internal resistance. You have just witnessed Ohm's law and the difference between an ideal and real source.
- Light an LED. Get a 5 V supply, an LED, a 330 Ω resistor. Wire them in series (anode to +, resistor to GND). It lights. Reverse the LED — it does not. You just observed a band-gap-determined emission and the rectifying behavior of a pn-junction.
- Open an old wall-wart power adapter. (One you do not need!) You will see a transformer (Faraday's law), a bridge rectifier (four diodes), a smoothing capacitor, and probably a regulator chip. Every concept of this chapter is present.
- Look up the datasheet of any modern microcontroller (STM32F411, RP2040, ATmega328p — any of them). Search for "ESD protection." Notice the diagram showing diodes from each pin to VDD and GND. Those diodes exist because of Coulomb's law and the inevitability of static electricity.
- Run a tunneling-current calculation on a 1 nm SiO₂ gate oxide at 1 V bias. (Search for the WKB tunneling formula.) See for yourself why scaling below this oxide thickness was impossible without changing the dielectric.
When the above feel comfortable — when you can explain to a friend why coax keeps signals in, why your AA battery only delivers 1.5 V, and why a flash drive eventually forgets — you have the physics chapter under your belt. Onward to Chapter 1: Electronic Devices and Circuits, where we make these ideas walk and talk as diodes and transistors.