Knowledge Organiser: Lenses and Images
Part of Lenses & Images · GCSE GCSE Physics revision
This topic summary covers Knowledge Organiser: Lenses and Images within Lenses & Images for GCSE Physics. Revise Lenses & Images in Waves for GCSE Physics with 13 exam-style questions and 15 flashcards. This is a high-frequency topic, so it is worth revising until the explanation feels precise and repeatable. It is section 14 of 14 in this topic. Use this topic summary to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 14 of 14
Practice
13 questions
Recall
15 flashcards
Knowledge Organiser: Lenses and Images
Key Terms
- Convex: converging, thicker in middle
- Concave: diverging, thinner in middle
- Focal point F: where parallel rays converge
- Real image: rays meet, can project, inverted
- Virtual image: rays appear to meet, upright, cannot project
Image Summary (Convex Lens)
- Beyond 2F → real, inverted, diminished
- At 2F → real, inverted, same size
- Between F and 2F → real, inverted, magnified
- Closer than F → virtual, upright, magnified
Key Equations
- Magnification = image height ÷ object height
- No units for magnification
Exam Tips
- Three characteristics: real/virtual, upright/inverted, magnified/diminished
- Use three rays for ray diagrams (parallel, centre, through F)
- Short-sight → concave; long-sight → convex
- Virtual images CAN be seen, just not projected
Common Mistakes
- Describing images with only one characteristic: Always give all three — real/virtual, upright/inverted, and magnified/diminished — for full marks in image description questions
- Confusing short-sight and long-sight corrections: Short-sighted (can't see far) → diverging (concave) lens; long-sighted (can't see near) → converging (convex) lens
- Saying virtual images cannot be seen: Virtual images cannot be projected onto a screen but they can be seen by the eye — a plane mirror produces a virtual image you can clearly see
- Drawing ray diagrams without using principal rays: Use the three standard rays (parallel to axis, through centre, through focal point) to accurately locate the image — guessing the image position loses marks
- Confusing focal length and focal point: The focal point (F) is where parallel rays converge; the focal length is the distance from the lens centre to F — power (D) = 1 ÷ focal length (m)
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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.
Quick Recall Flashcards
13 questions on Lenses & Images — practise free
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