The Waves section covers general wave properties, light (reflection, refraction, lenses), sound, and the electromagnetic spectrum. It combines theory with practical applications like optical instruments and communication.
Transverse: displacement perpendicular to travel (light, water). Longitudinal: displacement parallel to travel (sound). Wave equation: v = fλ. Period T = 1/f. Amplitude determines energy. Diffraction: waves spread around obstacles and through gaps (most when gap ≈ wavelength).
Reflection: angle of incidence = angle of reflection (measured from normal). Image in plane mirror: same size, laterally inverted, virtual, same distance behind mirror. Refraction: light bends towards the normal when entering a denser medium (slower speed). Refractive index n = sin i / sin r. Total internal reflection when angle > critical angle (sinc = 1/n). Applications: optical fibres, prisms.
Longitudinal wave — needs a medium (cannot travel through vacuum). Speed in air ≈ 340 m/s. Pitch depends on frequency (higher frequency = higher pitch). Loudness depends on amplitude. Echoes: reflection of sound. Ultrasound (>20 kHz): medical imaging, sonar. Human hearing: 20 Hz to 20 kHz.
All EM waves travel at c = 3 × 10⁸ m/s in vacuum. Order (low to high frequency): radio, microwave, infrared, visible, ultraviolet, X-ray, gamma. Uses: radio (broadcasting), microwave (cooking, mobile phones), IR (remote controls, heating), UV (sterilisation), X-rays (medical imaging), gamma (cancer treatment). Dangers increase with frequency.
Light travels slower in glass than in air. When it enters glass at an angle, the part of the wavefront that enters first slows down while the rest is still travelling fast in air. This causes the wavefront to change direction — bending towards the normal (the denser medium slows the wave). The greater the difference in speed, the greater the bending. This is described quantitatively by Snell\'s law: n₁ sin θ₁ = n₂ sin θ₂.
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