Building Blocks: Waves — AQA Combined Science: Synergy
Waves transfer energy and information without transferring matter. This topic covers wave types, the wave equation and electromagnetic waves.
Transverse and longitudinal waves
- Transverse waves — oscillations are perpendicular to the direction of energy transfer (e.g. electromagnetic waves, water ripples).
- Longitudinal waves — oscillations are parallel to the direction of energy transfer, forming compressions and rarefactions (e.g. sound).
In both, particles only vibrate about a fixed point — matter is not transferred.
Describing waves
- Amplitude — maximum displacement from rest.
- Wavelength (λ) — distance between corresponding points on adjacent waves.
- Frequency (f) — waves per second, in hertz (Hz).
- Period (T) — time for one wave: $T = 1/f$.
The wave equation
$$v = f \times \lambda$$ (wave speed = frequency × wavelength, in m/s)
Required practical: measuring the wavelength, frequency and speed of waves in a ripple tank and on a stretched string.
Electromagnetic waves
EM waves are transverse and all travel at the same speed in a vacuum (the speed of light). The spectrum, from longest wavelength to shortest:
Radio → Microwave → Infrared → Visible → Ultraviolet → X-rays → Gamma
Uses
- Radio — broadcasting and communications.
- Microwaves — cooking, satellite communications.
- Infrared — heating, cooking, remote controls, thermal imaging.
- Visible — seeing.
- Ultraviolet — security marking, tanning, fluorescent lamps.
- X-rays — medical imaging of bones.
- Gamma — sterilising equipment, treating cancer.
Hazards
The higher-frequency waves are ionising: UV can cause skin cancer; X-rays and gamma can mutate genes and cause cancer.
Radio waves (Higher Tier)
Radio waves can be produced by oscillations in electrical circuits. When absorbed, they can create an alternating current of the same frequency — the basis of radio reception.
Reflection and refraction (Higher Tier)
At a boundary, waves can be reflected, transmitted (refracted) or absorbed. In reflection the angle of incidence equals the angle of reflection. Refraction is the change in direction when a wave changes speed crossing a boundary.
Exam tips
- Distinguish transverse and longitudinal waves with examples (light vs sound).
- Learn v = fλ and T = 1/f, and practise rearranging and converting (kHz, MHz).
- Memorise the EM spectrum in order with uses and hazards.
- All EM waves are transverse and travel at the same speed in a vacuum.