Waves covers wave properties and behaviour — types, the wave equation, reflection, refraction, diffraction, the electromagnetic spectrum, and sound — key concepts for understanding light, communication, and imaging.
Transverse: oscillation perpendicular to direction of travel (light, water). Longitudinal: oscillation parallel (sound, ultrasound). Key terms: amplitude (maximum displacement), wavelength λ (one complete cycle), frequency f (cycles per second, Hz), period T = 1/f. Wave equation: v = fλ (speed = frequency × wavelength). Reflection: angle of incidence = angle of reflection. Refraction: wave changes speed and direction at a boundary. Diffraction: waves spread through gaps (most when gap ≈ wavelength).
Sound: longitudinal wave, needs a medium (cannot travel in vacuum). Speed in air ≈ 340 m/s. Human hearing: 20 Hz – 20 kHz. Ultrasound (> 20 kHz): medical imaging, sonar. Echo: distance = speed × time / 2. EM spectrum (all transverse, travel at 3×10⁸ m/s in vacuum): radio, microwave, infrared, visible, ultraviolet, X-ray, gamma. Uses and dangers for each. Total internal reflection: when angle > critical angle in denser medium; used in optical fibres and prisms.
Light bends (refracts) at the boundary because it changes speed. Light travels slower in glass (denser medium) than in air. When light enters glass at an angle, the part of the wavefront that hits the glass first slows down while the part still in air continues at the faster speed — this causes the wave to change direction. The ray bends toward the normal (the line perpendicular to the surface). Snell\'s law describes this: n₁ sinθ₁ = n₂ sinθ₂, where n is the refractive index. If light enters along the normal (angle = 0°), it slows down but doesn\'t bend.
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