Wave Properties and the EM Spectrum

GCSE Physics · Waves

Key wave terms

Amplitude – maximum displacement from rest (links to energy/loudness/brightness).
Wavelength (λ) – distance between matching points (metres).
Frequency (f) – waves per second, in hertz (Hz).
Period (T) – time for one wave: T = 1 / f.

The wave equation

wave speed = frequency × wavelength      v = f × λ

Worked example

A wave of frequency 50 Hz and wavelength 4 m:

v = f × λ = 50 × 4 = 200 m/s

Transverse vs longitudinal

Transverse – vibrations perpendicular to travel (light, water, all EM waves).
Longitudinal – vibrations parallel to travel (sound), with compressions and rarefactions.

The electromagnetic spectrum (low → high frequency)

Radio → Microwave → Infrared → Visible → Ultraviolet → X-ray → Gamma

All travel at the speed of light in a vacuum (3 × 10⁸ m/s). Higher frequency = more energy = more dangerous (UV, X-ray, gamma can damage cells / cause cancer).

Uses

Radio (broadcasting), microwave (cooking, satellites), IR (heating, remotes), visible (sight), UV (sun beds, detecting forgeries), X-ray (imaging bones), gamma (sterilising, treating cancer).

Exam tip

Mnemonic for the order: "Raging Martians Invaded Venus Using X-ray Guns." Remember v = f λ for calculations.