Chapter 12: Waves

Progressive waves transfer energy through space by causing particles in a medium to oscillate around their equilibrium positions, and students learn to characterize waves using displacement, amplitude, wavelength, period, and frequency, with frequency measured in hertz and related inversely to period. The chapter distinguishes between two fundamental wave types: longitudinal waves, where particle motion occurs parallel to energy propagation and include sound, and transverse waves, where particles move perpendicular to the direction of travel, encompassing light and electromagnetic radiation. The concept of phase difference quantifies how oscillations at different points along a wave relate to one another, with particles separated by one complete wavelength vibrating in phase. Wave energy transmission is analyzed through intensity, defined as power per unit area perpendicular to wave velocity and proportional to the square of amplitude, while wave speed emerges from the fundamental relationship between frequency and wavelength. The Doppler effect explains the observed frequency shift when sources move relative to observers, with approaching sources producing higher frequencies and receding sources producing lower frequencies, calculated through a specific mathematical formula accounting for source velocity and wave speed. Electromagnetic waves, composed of oscillating electric and magnetic fields perpendicular to each other and to their direction of propagation, all travel at the constant speed of light in vacuum, allowing the electromagnetic spectrum to be organized by wavelength from radio waves through visible light to gamma rays. Finally, polarization, a property exclusive to transverse waves, describes the restriction of vibration to a single plane, and Malus's Law quantifies how the intensity of polarized light decreases with the square of the cosine of the angle between transmission axes.