Lenses (Physics only)

    AQA
    GCSE

    Lenses exploit the refraction of light to manipulate wavefronts, utilizing convex (converging) and concave (diverging) geometries to form images. Mastery requires the construction of precise ray diagrams to determine image nature—real or virtual, upright or inverted, magnified or diminished—based on object placement relative to the principal focus. Quantitative assessment involves the application of the magnification formula and the Gaussian lens formula to predict image position and size. These principles underpin the function of optical systems, including the human eye, cameras, and corrective vision technologies.

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    Objectives
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    Exam Tips
    4
    Pitfalls
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    Key Terms
    5
    Mark Points

    What You Need to Demonstrate

    Key skills and knowledge for this topic

    • Award 1 mark for a ray drawn parallel to the principal axis refracting through the principal focus (F) on the other side of the lens
    • Award 1 mark for a ray passing through the optical centre continuing in a straight line without deviation
    • Credit responses that describe the image using all three required descriptors: size (magnified/diminished), orientation (upright/inverted), and nature (real/virtual)
    • Award 1 mark for correct substitution into the magnification formula M = image height / object height, ensuring units are consistent
    • For virtual images, credit dashed lines projected backward from the refracted rays to the point of intersection

    Marking Points

    Key points examiners look for in your answers

    • Award 1 mark for a ray drawn parallel to the principal axis refracting through the principal focus (F) on the other side of the lens
    • Award 1 mark for a ray passing through the optical centre continuing in a straight line without deviation
    • Credit responses that describe the image using all three required descriptors: size (magnified/diminished), orientation (upright/inverted), and nature (real/virtual)
    • Award 1 mark for correct substitution into the magnification formula M = image height / object height, ensuring units are consistent
    • For virtual images, credit dashed lines projected backward from the refracted rays to the point of intersection

    Examiner Tips

    Expert advice for maximising your marks

    • 💡Always use a sharp pencil and ruler for ray diagrams; AQA examiners penalize thick or wavy lines that obscure the precise intersection point
    • 💡Memorize the rule for concave lenses: they ALWAYS produce images that are virtual, upright, and diminished, regardless of object position
    • 💡When calculating magnification, if the image is virtual/upright, do not include a negative sign unless specifically working with advanced sign conventions (rare in GCSE); focus on the ratio of heights
    • 💡Check your image description against the object position: if the object is outside 2F, the image must be real, inverted, and diminished

    Common Mistakes

    Pitfalls to avoid in your exam answers

    • Drawing light rays without directional arrows, leading to loss of marks for the ray path
    • Failing to extend diverging rays backwards with dashed lines to locate a virtual image, often leaving the diagram incomplete
    • Confusing the principal focus (F) with the centre of curvature (2F) when drawing the ray passing through the focus
    • Stating that a virtual image can be projected onto a screen, demonstrating a fundamental misconception of image nature

    Key Terminology

    Essential terms to know

    Likely Command Words

    How questions on this topic are typically asked

    Draw
    Describe
    Calculate
    Explain
    Compare

    Practical Links

    Related required practicals

    • •{"code":"Required Practical 9","title":"Investigation of Reflection and Refraction","relevance":"Foundational skills in ray tracing and measuring angles of incidence/refraction apply directly to lens diagrams"}

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