AQA GCSE Physics 4.6 Waves: a complete overview of wave types, properties, the EM spectrum, reflection, sound and lenses

What topic 4.6 actually demands

Waves links a small set of definitions and one key equation to a wide range of applications, from communications to medicine. AQA tests precise definitions, the wave speed calculation, the order and uses of the electromagnetic spectrum, and clear reasoning about reflection, refraction and sound.

This guide walks through all six dot points of the topic, then sets out the exam patterns AQA repeats. Each dot point has a matching page with practice questions; this overview ties them together.

Wave types and properties

Waves transfer energy, not matter. Transverse waves oscillate perpendicular to the energy transfer (all EM waves, water ripples); longitudinal waves oscillate parallel to it, with compressions and rarefactions (sound). The properties are amplitude, wavelength, frequency and period, linked by $T = \frac{1}{f}$ and the wave speed equation $v = f\lambda$. The required practical measures wave speed in a ripple tank and on a string.

The electromagnetic spectrum

The EM spectrum is one continuous family of transverse waves travelling at the same speed in a vacuum. In order of increasing frequency: radio, microwaves, infrared, visible light, ultraviolet, X-rays, gamma rays. Each has uses (broadcasting, cooking, heating, seeing, security marking, medical imaging, sterilising and cancer treatment), and the highest-frequency waves are ionising and dangerous.

Reflection and refraction

At a boundary a wave can be reflected, transmitted or absorbed. The law of reflection says the angle of incidence equals the angle of reflection. Specular reflection (smooth surface) gives a clear image; diffuse reflection (rough surface) scatters. Refraction is a change in direction caused by a change in speed: a wave slowing down bends towards the normal.

Sound and ultrasound

Sound is longitudinal and needs a medium, so it cannot travel through a vacuum. The hearing range is about $20\,Hz$ to $20\,kHz$. Ultrasound (above $20\,kHz$) is used for prenatal scanning and flaw detection, and reflected waves are used in echo sounding and to study the Earth with seismic waves.

Lenses and visible light

A convex lens converges rays and a concave lens diverges them; magnification is image height over object height. The colour of an opaque object is the colour it reflects, absorbing the rest; a filter transmits only its own colour.

How topic 4.6 is examined

A typical AQA profile for Waves:

• Definitions. Wave types, amplitude, wavelength, frequency and period.
• Calculations. The wave speed equation, period, and magnification.
• Recall and application. The EM spectrum order, uses and dangers, the law of reflection, and ultrasound uses.
• Extended answers. Explaining refraction, how sound is heard, and how the colour of objects arises.

Check your knowledge

A mix of recall and calculation questions covering topic 4.6. Attempt them under timed conditions, then check against the solutions.

1. State the difference between a transverse and a longitudinal wave. (2 marks)
2. Define the wavelength of a wave. (1 mark)
3. A wave has a frequency of $25\,Hz$ and a wavelength of $0.8\,m$. Calculate its speed. (2 marks)
4. List the seven groups of the EM spectrum in order of increasing frequency. (2 marks)
5. State one use and one danger associated with the EM spectrum. (2 marks)
6. State the law of reflection. (1 mark)
7. State the approximate human hearing range and define ultrasound. (2 marks)
8. An object $4\,cm$ tall produces an image $10\,cm$ tall. Calculate the magnification. (2 marks)