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define / state / describe / determine
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(a) Define the principal focus of a converging lens. (b) A parallel beam of light passes through a converging lens of focal length 6.5 cm. State how far from the lens the rays cross the principal axis, and describe what a screen 13 cm behind the lens shows. (c) An object stands on the principal axis exactly at the principal focus of a converging lens. From its tip, a pupil draws the ray parallel to the axis and the ray through the centre of the lens. Describe how these two rays leave the lens, and state what this tells you about the image. (d) A converging lens of focal length 25 cm forms a real, enlarged image of a small toy figure on a screen. Determine the range of distances from the lens in which the figure must be.
define: give the precise meaning. state: give a concise answer. describe: give the features or what happens. determine: find the answer from the information given.
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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