This is the second in a series of computer science lessons about wireless communication and digital signal processing. In these lessons you’ll learn about the nature of electromagnetic radiation, digital modulation and multiplexing techniques, and how to get the best out of mobile communication systems such as LTE, 5G and WiFi. This lesson takes a brief look at the properties and behaviours of electromagnetic waves. It begins with a description of the well-known bands of the electromagnetic spectrum including cosmic rays, gamma rays, x rays, ultraviolet, infrared, visible light, microwaves and of course radio waves. The lesson then describes effects such as reflection, scattering, diffraction, refraction and absorption. In particular the impact of these effects on the propagation of radio signals is discussed. Chapters: 00:00 The electromagnetic spectrum 02:36 Reflection 03:03 Scattering 03:25 Sky waves 03:41 Diffraction 04:40 Refraction 05:32 Tropospheric ducting 05:53 Absorption