Contents
Independent final check
Explain without the key
define / determine / describe
Final check
(a) Define the focal length of a lens. (b) Define the principal axis of a lens. (c) An object 3.0 cm tall stands on the principal axis 30 cm from a converging lens of focal length 12 cm. On paper, draw a ray diagram at half size. Determine how far from the lens the image is and how tall it is, in real centimetres. (d) Describe the image.
define: give the precise meaning. determine: find the answer from the information given. describe: give the features or what happens.
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Scope and sources
Cambridge IGCSE Physics 0625 · 2026–2028 v2 · Original learning materials.
The action of thin converging and diverging lenses on a parallel beam of light (3.2.3.1); focal length, principal axis and principal focus (3.2.3.2); ray diagrams for the formation of a real image by a converging lens (3.2.3.3); describing an image as enlarged, same size or diminished, upright or inverted, real or virtual (3.2.3.4); a virtual image formed when diverging rays are extrapolated backwards, which cannot be projected onto a screen (3.2.3.5); Supplement: ray diagrams for a virtual image formed by a converging lens (3.2.3.6), a single lens as a magnifying glass (3.2.3.7), and converging and diverging lenses correcting long-sightedness and short-sightedness (3.2.3.8). The lens equation and lens power are not in the syllabus; ray diagrams for images formed by a diverging lens are not drawn here; the structure of the eye is in Biology; dispersion of light is in Light and the electromagnetic spectrum.
Apparatus, amounts and times in the experiment are illustrative. Real practical work follows a teacher-approved safety method.
Official Cambridge syllabus