electromagnetic spectrum

Meaning: Electromagnetic waves are transverse oscillations of electric and magnetic fields that need no medium. The spectrum arranges them from low frequency and long wavelength (radio, microwave, infrared) through visible light to high frequency and short wavelength (ultraviolet, X-ray, gamma). Visible light is a narrow band, roughly 400 nm (violet) to 700 nm (red). Photon energy rises toward the gamma end.

Equation: c = fλ and E = hf, where c = 3.00 × 10⁸ m/s is the speed of light in vacuum, f is frequency (Hz), λ is wavelength (m), E is photon energy (J), and h = 6.63 × 10⁻³⁴ J·s is Planck's constant.

On the MCAT: You may be asked to rank regions by frequency, wavelength or photon energy, or to predict what happens to one when another changes. Passages link regions to techniques: infrared to bond vibrations, UV-visible to electronic transitions, radio waves to NMR. Photoelectric effect questions use E = hf.

Common confusion: Students think higher-frequency light travels faster. In vacuum every region moves at c, so higher frequency simply means shorter wavelength. In a medium the speed drops to c/n, and the frequency stays fixed while the wavelength changes.