Chapter 20 -- The Energy of Waves (the nature of waves / properties of waves / wave interactions)
Chapter 21 -- The Nature of Sound (what is sound / properties of sound / interactions of sound waves / sound quality)
Chapter 22 -- The Nature of Light (what is light / electromagnetic spectrum / interactions of light waves / light and color)
Chapter 23 -- Light and Our World (mirrors and lenses / light and sight / light and technology) notes