Waves and Optics

Waves are one of the most important concepts in physics. They transfer energy without transferring matter, and their behaviour underpins everything from sound and light to quantum mechanics. This topic covers progressive and stationary waves, the electromagnetic spectrum, refraction, diffraction, interference, and polarisation.

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Progressive Waves

A progressive (or travelling) wave carries energy from one place to another. Key terminology:

Key Definition: Amplitude (A) — the maximum displacement of a particle from its equilibrium position.

Key Definition: Wavelength (λ) — the minimum distance between two points oscillating in phase (e.g. crest to crest).

Key Definition: Frequency (f) — the number of complete oscillations per second, measured in hertz (Hz).

• Period (T) — the time for one complete oscillation: T = 1/f
• Wave speed (v) — the speed at which the wavefront travels: v = fλ

Transverse and Longitudinal Waves

• Transverse waves — the oscillation is perpendicular to the direction of energy transfer. Examples: electromagnetic waves, water waves, waves on a string, S-waves (seismic).
• Longitudinal waves — the oscillation is parallel to the direction of energy transfer. Examples: sound waves, P-waves (seismic), compression waves in a spring.