Waves covers the behaviour of progressive and stationary waves, and the phenomena of diffraction, interference, and the Doppler effect — combining theory with practical experiments.
Transfer energy without transferring matter. v = fλ. Transverse: displacement perpendicular to propagation (light, water, strings). Longitudinal: displacement parallel (sound, longitudinal spring). Intensity I ∝ A² (proportional to amplitude squared). Also I = P/A (power per unit area, W/m²). Phase difference: 0° (in phase), 180° (antiphase), measured in radians. Polarisation: transverse waves only — vibration restricted to one plane. Evidence that light is transverse. Applications: Polaroid filters, LCD screens, reducing glare.
Formed by superposition of two progressive waves of same frequency travelling in opposite directions. Nodes: zero displacement (destructive interference). Antinodes: maximum displacement (constructive). No energy transfer. String: fundamental frequency f₁ = v/2L. Harmonics: f₂ = 2f₁, f₃ = 3f₁. Air columns: open pipe: all harmonics. Closed pipe: odd harmonics only. Measure speed of sound using resonance tube.
Superposition: when waves meet, displacements add. Constructive: waves in phase → larger amplitude. Destructive: waves in antiphase → zero/reduced amplitude. Coherence: same frequency, constant phase difference — required for observable interference. Young\'s double slit: λ = ax/D (a = slit separation, x = fringe spacing, D = distance to screen). Diffraction grating: d sinθ = nλ (sharper maxima). Single slit diffraction: central maximum wider than secondary maxima.
Coherent sources have the same frequency and a constant phase difference. This is needed because interference requires a stable pattern of constructive and destructive regions. If the frequency or phase relationship changes randomly (as with two independent light bulbs), the interference pattern shifts rapidly and randomly — our eyes see an average of bright and dark, which appears as uniform illumination. Lasers produce coherent light naturally. Alternatively, a single source can be split into two coherent beams (as in Young\'s experiment using a single slit before the double slit).
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