# Waves

> CIE IGCSE Physics · CIE IGCSE Physics (0625)
> Source: https://www.owlsprep.com/study/cie-0625-u3-overview/
> Weight: 12-15% of total assessment, split across MCQ, structured and extended response questions

This unit introduces core wave phenomena, from universal wave properties to specific applications of light, electromagnetic radiation, and sound, aligned to the full 0625 syllabus requirements.

**Prerequisites:** [CIE IGCSE Physics Unit 1: Measurements, Units and Motion](https://www.owlsprep.com/study/cie-0625-u1-overview/)

## Learning objectives

- Describe core wave properties including amplitude, wavelength, frequency, period and wave speed, and solve problems using the wave equation
- Explain reflection, refraction of light, and image formation by thin lenses, including drawing accurate ray diagrams
- Recall the properties, uses, and safety hazards of all segments of the electromagnetic spectrum
- Describe the production, propagation, and practical applications of sound waves, including ultrasound

## Unit at a Glance

The unit follows a logical learning arc: you will first master universal wave characteristics and behaviors, then apply these fundamentals to optical phenomena (light reflection, refraction, lenses), before moving to the electromagnetic spectrum and sound waves. Each subtopic builds directly on content from the prior one, so work through them in order to avoid gaps in understanding.

All content is tailored to common exam question scenarios, with clear links between abstract theory and real-world applications that are frequently tested in the 0625 assessment.

Work through the subtopics in the order listed below to build mastery incrementally:
- [General Properties of Waves](https://www.owlsprep.com/study/cie-0625-u3-general-properties-of-waves/) — Defines core wave parameters, the wave equation, and universal wave behaviors including reflection, refraction and diffraction.
- [Reflection and Refraction of Light](https://www.owlsprep.com/study/cie-0625-u3-reflection-and-refraction-of-light/) — Explores the law of reflection, plane mirror ray diagrams, Snell’s law, and total internal reflection applications.
- [Thin Lenses](https://www.owlsprep.com/study/cie-0625-u3-thin-lenses/) — Covers converging/diverging lens ray diagrams, image characteristics, magnification calculations and practical lens uses.
- [Dispersion and the Electromagnetic Spectrum](https://www.owlsprep.com/study/cie-0625-u3-dispersion-and-the-electromagnetic-spectrum/) — Explains white light dispersion, properties of each EM spectrum segment, and their real-world uses and safety hazards.
- [Sound](https://www.owlsprep.com/study/cie-0625-u3-sound/) — Describes sound wave production, propagation, speed measurement, echoes, ultrasound applications and the human auditory range.

## Common pitfalls

- **Wrong:** Confusing wave speed, frequency and wavelength when a wave enters a new medium
  - Why it fails: Frequency of a wave does not change when crossing media, only speed and wavelength adjust
  - Correct: Use $v = f\\times\lambda$: if speed decreases in a denser medium, wavelength decreases proportionally while frequency stays constant
- **Wrong:** Drawing converging lens ray diagrams with incorrect ray paths for objects inside the focal length
  - Why it fails: This leads to misidentifying if an image is real/virtual, upright/inverted or magnified/reduced
  - Correct: Always draw the three standard rays: parallel to axis through focus, through lens center unchanged, through near focus parallel to axis
- **Wrong:** Mixing up uses of ultraviolet and infrared radiation in the EM spectrum
  - Why it fails: Both have common daily/industrial applications that are high-frequency exam questions
  - Correct: Link properties to uses: UV causes fluorescence, IR is used for thermal imaging and heating

## Cheatsheet

| Name | Formula/Key Rule | Subtopic |
| --- | --- | --- |
| Wave Equation | $v = f\times\lambda$ (speed = frequency × wavelength) | General Properties of Waves |
| Law of Reflection | Angle of incidence = Angle of reflection, measured to the normal | Reflection and Refraction of Light |
| Snell’s Law | $n = \frac{\sin i}{\sin r}$ (refractive index = sin(incidence angle)/sin(refraction angle)) | Reflection and Refraction of Light |
| Describing an Image (Lenses) | Use enlarged / same size / diminished, upright / inverted and real / virtual (no magnification formula at IGCSE) | Thin Lenses |
| EM Spectrum Order (lowest to highest frequency) | Radio, Microwave, Infrared, Visible, Ultraviolet, X-Ray, Gamma Ray | Dispersion and the Electromagnetic Spectrum |
| Speed of Sound in Air | ~330 m/s at standard room temperature | Sound |

## What's next

Begin your study of this unit with the first subtopic: General Properties of Waves, which establishes the foundational vocabulary and equations you will use for all subsequent wave-related content. Once you have completed all subtopics in Unit 3, move on to Unit 4: Electricity and Magnetism, another high-weight area of the 0625 syllabus covering circuits, magnetic fields and electromagnetism.

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From [OwlsPrep](https://www.owlsprep.com) — free study guides for A-Level, IB, AP and IGCSE, written against the official syllabus. Canonical page: https://www.owlsprep.com/study/cie-0625-u3-overview/