Electromagnetic spectrum

Essential knowledge 14.4.A.3 sets the organising principle: categories of electromagnetic waves are characterized by their wavelengths. EK 14.4.A.3.i gives the list, in order of decreasing wavelength and spanning a range from kilometres to picometres.

Radio waves, microwaves, infrared, visible, ultraviolet, X-rays, gamma rays.

Visible light is subdivided the same way in EK 14.4.A.3.ii, again by decreasing wavelength: red, orange, yellow, green, blue, violet.

How deep to learn it. The Topic 14.4 boundary statement is explicit. AP Physics 2 expects students to know the ordering of the electromagnetic spectrum, including visible light. However, students will not be expected to define exact wavelength ranges within the spectrum. Learn the sequence; do not memorise nanometre bands.

Two quantities run backwards along the list. The sheet prints $\lambda = c/f$ in the Modern Physics group, so decreasing wavelength means increasing frequency. It also prints $E = hf$, so the same direction means increasing photon energy. Gamma rays sit at the short, fast, energetic end and radio waves at the long, slow, gentle end, and that ordering is the reason the two ends behave so differently in matter.

One spectrum, one speed. Every category travels at $c = 3.00 \times 10^8$ m/s in vacuum (14.1.A.3.i). The categories are names for wavelength ranges of a single kind of wave, not different kinds of wave. EK 14.4.A.3.iii notes that all of them are sometimes collectively called light, or electromagnetic radiation.