Reflection

    OCR
    GCSE

    Reflection describes the change in direction of a wavefront at an interface between two different media so that the wavefront returns into the medium from which it originated. The fundamental Law of Reflection states that the angle of incidence equals the angle of reflection, measured relative to the normal. Candidates must demonstrate proficiency in constructing ray diagrams to locate virtual images in plane mirrors, ensuring object distance equals image distance. Furthermore, the distinction between specular reflection on smooth surfaces and diffuse reflection on rough surfaces is critical for explaining how non-luminous objects are seen.

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    Objectives
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    Exam Tips
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    Pitfalls
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    Key Terms
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    Mark Points

    What You Need to Demonstrate

    Key skills and knowledge for this topic

    • Award 1 mark for drawing the normal as a dashed line perpendicular (90°) to the mirror surface at the point of incidence
    • Credit responses that explicitly state or show the angle of incidence equals the angle of reflection (i = r)
    • Award 1 mark for light rays drawn as continuous straight lines with a ruler, including arrows indicating direction
    • For virtual image diagrams, credit dashed lines projected behind the mirror converging at the image position
    • Award 1 mark for explaining diffuse reflection by referencing the uneven nature of the surface causing parallel rays to reflect in different directions

    Example Examiner Feedback

    Real feedback patterns examiners use when marking

    • "You have correctly drawn the rays, but check where you measured your angle from — remember the normal"
    • "Good definition of the law of reflection. Now apply this to explain why the image in a plane mirror appears 'behind' the glass"
    • "Your diagram is neat, but you missed the directional arrows. In Physics, a line without an arrow is just geometry, not a ray"
    • "Excellent distinction between specular and diffuse. To secure full marks, explicitly mention that the law of reflection holds true for individual rays in both scenarios"

    Marking Points

    Key points examiners look for in your answers

    • Award 1 mark for drawing the normal as a dashed line perpendicular (90°) to the mirror surface at the point of incidence
    • Credit responses that explicitly state or show the angle of incidence equals the angle of reflection (i = r)
    • Award 1 mark for light rays drawn as continuous straight lines with a ruler, including arrows indicating direction
    • For virtual image diagrams, credit dashed lines projected behind the mirror converging at the image position
    • Award 1 mark for explaining diffuse reflection by referencing the uneven nature of the surface causing parallel rays to reflect in different directions

    Examiner Tips

    Expert advice for maximising your marks

    • 💡Always bring a protractor and ruler; freehand sketches for ray diagrams are routinely penalized in OCR mark schemes
    • 💡When defining the 'normal', specify it is an imaginary line perpendicular to the surface at the point of incidence
    • 💡In 6-mark questions comparing specular and diffuse reflection, ensure you state that the law of reflection is obeyed in both cases

    Common Mistakes

    Pitfalls to avoid in your exam answers

    • Measuring the angle of incidence or reflection between the ray and the mirror surface instead of the normal
    • Drawing the normal as a solid object line rather than a dashed construction line
    • Stating that the law of reflection does not apply to diffuse reflection (it applies to every ray; the surface orientation changes)
    • Forgetting to add directional arrows to rays, leading to loss of marks in diagram questions

    Study Guide Available

    Comprehensive revision notes & examples

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    Key Terminology

    Essential terms to know

    Law of Reflection and the Normal
    Ray diagrams and Virtual Image formation
    Specular versus Diffuse reflection
    Lateral inversion and image characteristics

    Likely Command Words

    How questions on this topic are typically asked

    Draw
    Measure
    State
    Explain
    Describe
    Compare

    Practical Links

    Related required practicals

    • •{"code":"PAG 8","title":"Investigation of reflection and refraction","relevance":"Measuring angles of incidence and reflection using a ray box and plane mirror"}

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