Physical Science

This page is a collection of links and resources I have found useful/interesting and may want to refer back to sometime. Eventually, it will probably be broken into various sub sections, but until then…


Orbital Mechanics:



Communications - Wifi & Radio Spectrum


  1. All wireless technologies send and receive data via radio waves on specific frequencies in the radio spectrum.
  2. The radio spectrum is a frequency range (30 Hz to 300 GHZ) that exists on the electromagnetic spectrum
  3. The electromagnetic spectrum is the range of ALL frequencies that facilitate the propogation of electromagnetic radiation through space. Radio waves, infrared, visible light, and X-rays are all examples of electromagnetic radiation.
  • Frequencies are measured in Hertz units and are commonly expressed in multiples (1000x) of that base. For Example: Hertz (Hz) => Kilohertz (kHz) => Megahertz (MHz) => Gigahertz (GHz) => …

  • Radio waves, infrared and visible light are all related b/c they operate along the same frequency spectrum.

Radio Frequency Bands (Range):

Type Frequency
AM Radio ~550-1720 kHz
FM Radio ~88-108 MHz
Wifi ~2.4/5 GHz

Recall that: Hertz (Hz) => Kilohertz (kHz) => Megahertz (MHz) => Gigahertz (GHz) => …

So while the examples above can be expressed in any standard Hertz unit, the one you are used to seeing them with is generally more understandable.

Application Kilohertz Megahertz Gigahertz
AM Radio 550kHz 0.55MHz 0.00055GHz
FM Radio 88000kHz 88MHz 0.088GHz
Wifi (WLAN) 2400000kHz 2400MHz 2.4GHz

Why do FM stations in the US end in Odd Decimals

WIFI: Used to seeing it listed as 2.4GHz or 5GHz. Keep in mind this is actually operating in a range like FM radio.Recall that 2.4Ghz = 2400MHz. Wifi specifically operates in the 2401MHz - 2495Mhz ranges. This range is subdivided into channels, similar to radio, it’s just that typically software handles the channel selection, …not something the average consumer generally modifies.




  • Voltage, Current, Amps, etc…
  • Wet vs Dry Contacts
  • Wiring Basics:
    • Wire Coloring (US):
      • Black - This wire is considered “hot” or “live” and carrys electricity to the switch or outlet from the circuit breaker. A red wire may also be considered “hot” but is usually used in a secondary capacity.
      • White - This is the neutral wire
      • Green - This is the ground wire. It may also sometimes just be bare copper wiring without any insulation.
    • Line vs. Load - Implies directionality. The line wire “delivers” the electricity from the source (the circuit breaker, another outlet, etc.). The load carries the electricity downstream to other switches, outlets, etc)

Earth Sciences
  • Earthquake Magnitude Measurement - Moment Magnitude Scale - effectively supersedes Ritcher Scale - more accurate for larger magnitude earthequakes & more accurately measures a broader range of earthquake types across the globe.

Technolgy / Computing


Antikythera Mechanism