Who this is for: Cambridge IGCSE Coordinated Science (0654) students who want light — reflection, refraction, ray diagrams and the behaviour of light at boundaries — to become a reliable source of marks in diagram and explain questions.
What query it owns: how to understand and revise light in Cambridge IGCSE Coordinated Science.
Why this is safe: this page owns the light revision-guide angle, while Tutopiya’s Light subtopic page owns the learning resource and the free Light quiz owns the practice.

Light is a transverse electromagnetic wave that travels at approximately 3 × 10⁸ m/s in a vacuum. Cambridge IGCSE Coordinated Science (0654) expects you to draw ray diagrams for reflection and refraction, state the laws of reflection, and explain why light bends when entering a different medium. This guide links each behaviour to the draw, describe and explain questions examiners set.

Key takeaways

• Light travels in straight lines (rays) and reflects off surfaces.
• Law of reflection: angle of incidence = angle of reflection (measured from the normal).
• Refraction: light bends when entering a medium of different optical density.
• Light bends towards the normal entering a denser medium; away entering a less dense medium.
• Light is a transverse wave in the electromagnetic spectrum.

What is light in Cambridge IGCSE Coordinated Science?

Light enables us to see objects — either because they emit light (the Sun, a lamp) or because they reflect light into our eyes. When light hits a smooth surface, it reflects obeying the law of reflection. When light passes from one medium to another (e.g. air to glass), it changes speed and direction — this is refraction. Ray diagrams use straight lines with arrows to show the path of light. Examiners frequently test diagram drawing and explanation of bending at boundaries.

Study the ray diagrams and notes on Tutopiya’s Light subtopic page before attempting past-paper questions.

Reflection vs refraction

Feature	Reflection	Refraction
What happens	Light bounces off a surface	Light bends at a boundary between media
Key law	Angle of incidence = angle of reflection	Light slows/speeds up, changing direction
Normal	Perpendicular to surface at point of incidence	Perpendicular to boundary at point of entry
Examples	Mirror image, seeing a puddle	Pencil appearing bent in water, lenses
Diagram labels	Incident ray, reflected ray, normal	Incident ray, refracted ray, normal

How to draw a reflection ray diagram — step by step

1. Draw the surface (mirror or boundary) as a straight line.
2. Draw the normal (dashed line) perpendicular to the surface at the point of incidence.
3. Draw the incident ray approaching the surface; label the angle of incidence (i).
4. Draw the reflected ray on the other side of the normal with equal angle (r = i).
5. Check your diagram skills with the free Light quiz.

Light in past-paper wording: command words that matter

Command word / phrase	What the question wants	Typical light stem
Draw	Ray diagram with labels	”Draw a ray diagram to show reflection from a plane mirror.”
State	Law or fact	”State the law of reflection.”
Explain	Why light bends	”Explain why a ray of light bends when entering glass from air.”
Describe	What happens to light	”Describe what happens to light at a plane mirror.”

Worked exam-style stems (how to answer the wording)

1. “State the law of reflection.” The angle of incidence equals the angle of reflection, both measured from the normal to the surface. Reward: angle of incidence = angle of reflection + measured from normal.
2. “Explain why light bends towards the normal when entering glass from air.” Light travels slower in glass (a denser medium), so it changes direction; the part entering first slows down first, bending the ray towards the normal. Reward: slower in glass + direction change + towards normal.
3. “Draw a ray diagram showing reflection from a plane mirror.” Draw surface, normal, incident ray with angle i, reflected ray with angle r = i, all clearly labelled. Reward: correct angles + normal + labels.

Test yourself with the Light quiz once you can draw ray diagrams and explain refraction.

How light connects to the rest of Coordinated Science

Light builds on General Wave Properties (transverse waves, v = fλ) and leads to the Electromagnetic Spectrum (visible light as one region). The Cambridge IGCSE Coordinated Science resource hub links every Properties Of Waves subtopic.

Common mistakes students make

• Measuring angles from the surface instead of the normal.
• Drawing the reflected ray with an angle different from the incident angle.
• Saying light speeds up when entering glass from air (it slows down in denser media).
• Forgetting to label the normal on ray diagrams.
• Confusing reflection (bouncing off) with refraction (bending through).

When you need more support

If light ray diagram questions keep costing marks, work through the Light quiz, then get focused help from a Cambridge IGCSE Coordinated Science tutor.

Frequently asked questions

What is the law of reflection? The angle of incidence equals the angle of reflection, both measured from the normal.

Why does light refract? Light changes speed when entering a different medium, causing it to change direction at the boundary.

What is the speed of light in a vacuum? Approximately 3 × 10⁸ m/s.

How do I revise light effectively? Practise ray diagrams for reflection and refraction, then take the Light quiz.

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