This how it works covers How It Works: Drawing a Ray Diagram for a Convex Lens within Lenses & Images for GCSE Physics. Revise Lenses & Images in Waves for GCSE Physics with 13 exam-style questions and 15 flashcards. This topic appears less often, but it can still be a useful differentiator on mixed-topic papers. It is section 7 of 14 in this topic. Use this how it works to connect the idea to the wider topic before moving on to questions and flashcards.
⚙️ How It Works: Drawing a Ray Diagram for a Convex Lens
To find where an image forms, draw three standard rays from the top of the object:
- Ray 1 — Parallel to axis: Arrives at lens parallel to the principal axis → refracts through the far focal point (F)
- Ray 2 — Through centre: Passes straight through the centre of the lens without bending (the two surfaces are parallel at the centre, so no net refraction)
- Ray 3 — Through near focal point: Passes through the near focal point before the lens → exits the lens parallel to the principal axis
Where any two of these rays cross is where the real image forms. If the rays diverge on the far side, trace them back — where they appear to come from is a virtual image.
Practice questions for Lenses & Images
What does a convex (converging) lens do to parallel rays of light?
Explain the difference between a converging lens and a diverging lens. Include what each type does to parallel rays of light.