Wave properties, transverse vs longitudinal, the EM spectrum and its applications — everything on waves for GCSE Physics.
Waves carry energy from one place to another without transferring matter. At GCSE, waves covers a wide range of content — from basic wave properties and calculations through to the electromagnetic spectrum, reflection, refraction and sound. This guide builds the topic systematically, covering every concept and the calculations that accompany it.
All waves share the same set of properties:
Waves are classified by the relationship between the direction of oscillation and the direction of energy transfer.
Transverse waves: Oscillations are perpendicular (at right angles) to the direction of energy transfer. Examples: all electromagnetic waves (light, radio, X-rays), water waves, S-waves (secondary seismic waves). Can be represented as a sine wave on a diagram — the peaks and troughs are the oscillations.
Longitudinal waves: Oscillations are parallel to (along the same line as) the direction of energy transfer. The wave consists of compressions (regions of high pressure where particles are pushed together) and rarefactions (regions of low pressure where particles are spread apart). Examples: sound waves, P-waves (primary seismic waves). Cannot travel through a vacuum — they need a medium of particles to compress.
Sound cannot travel through a vacuum — it requires a medium of particles to transfer energy via compressions and rarefactions. Light can travel through a vacuum because electromagnetic waves do not require a medium. This is why space is silent but not dark.
When a wave hits a boundary and bounces back, it is reflected. The law of reflection states that the angle of incidence equals the angle of reflection — both measured from the normal (a line perpendicular to the reflecting surface at the point of incidence). A smooth surface produces specular (regular) reflection. A rough surface produces diffuse reflection — light scatters in many directions.
When a wave passes from one medium to another, its speed changes. If the wave enters at an angle, it also changes direction — this is refraction. Light slows down when entering a denser medium (e.g. glass) and bends toward the normal. It speeds up when entering a less dense medium and bends away from the normal.
The key rule: if speed decreases, the wave bends toward the normal. If speed increases, it bends away. Frequency never changes during refraction — only speed and wavelength change.
All electromagnetic (EM) waves travel at the same speed in a vacuum: 3 × 10⁸ m/s (the speed of light). They are transverse waves. They are arranged in order of frequency (and wavelength) in the electromagnetic spectrum.
In order of increasing frequency (decreasing wavelength): radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, gamma rays. A useful mnemonic: Reckless Monkeys Invent Very Unusual X-ray Guns.
Ionising radiation has enough energy to remove electrons from atoms, creating ions. This can damage DNA and cause cancer. Gamma rays, X-rays and high-frequency UV are ionising. Radio waves, microwaves, IR and visible light are non-ionising — they can still cause heating effects but cannot ionise atoms. This distinction is directly tested in exam questions about hazards.
Sound is a longitudinal mechanical wave. It requires a medium — it travels fastest through solids (particles closely packed, strong forces), slower through liquids, slowest through gases. Speed of sound in air ≈ 340 m/s. Speed of sound in water ≈ 1500 m/s. Speed of sound in steel ≈ 5000 m/s.
The pitch of a sound corresponds to its frequency — higher frequency gives higher pitch. The loudness corresponds to amplitude — greater amplitude gives louder sound. The human ear can detect frequencies between approximately 20 Hz and 20,000 Hz. Ultrasound is above 20,000 Hz — used in medical imaging (foetal scans, detecting internal injuries) and sonar.
The AQA waves specification is at the AQA GCSE Physics specification page.
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