GCSE Physics: Reflection, Refraction, Lenses and Colour

This material takes the waves topic of GCSE Physics beyond the wave equation and the electromagnetic spectrum, and focuses on how light behaves. Reflection and refraction at boundaries are shared with combined science; lenses, visible light and colour, and black-body radiation are separate (triple) physics content, for example in AQA's specification.

You start with what can happen when light meets a boundary: it can be reflected, absorbed or transmitted. You distinguish specular reflection from a smooth surface, which gives a clear image, from diffuse reflection from a rough surface, which scatters light in many directions, and you describe refraction as light enters glass at an angle: it slows down and bends towards the normal, while a ray along the normal carries straight on.

The lens questions ask you to describe images in the standard three terms: real or virtual, upright or inverted, magnified or diminished. A convex lens with a distant object gives a real, inverted, diminished image, as in a camera, while an object closer than the principal focus gives a virtual, upright, magnified image, as in a magnifying glass. A concave lens always gives a virtual, upright, diminished image. Magnification is image height divided by object height, has no units, and needs both heights in the same unit, so one calculation mixes millimetres and centimetres on purpose.

The colour section explains why an opaque object looks the colour it does (it reflects that colour and absorbs the rest), why a red object looks black under blue light, and how colour filters transmit their own colour and absorb the others. The last section is about black-body radiation: a perfect black body absorbs all the radiation falling on it and is the best emitter, a hotter body emits more radiation with more of it at shorter wavelengths, and, at Higher tier, the temperature of the Earth depends on the balance between the radiation it absorbs and emits.

The material offers three formats. The quiz has 12 questions mixing single-answer and multiple-answer items, each with an explanation. The flashcards give quick revision of image descriptions and definitions. The written work is a printable sheet of 8 longer questions, including wave-front explanations of refraction, magnification calculations and colour predictions, which you answer by hand and upload for feedback on each answer.

• Describe what can happen to light at a boundary and distinguish specular from diffuse reflection
• Explain refraction at a glass surface, including (Higher) with wave fronts
• Describe the images formed by convex and concave lenses as real/virtual, upright/inverted, magnified/diminished
• Calculate magnification from image and object heights, converting units where needed
• Predict the colour of objects under coloured light and through filters
• Explain black-body radiation and (Higher) how the Earth's temperature depends on absorbed and emitted radiation

Practice material written by Zestly, based on the DfE GCSE physics subject content (waves: reflection, refraction, lenses, visible light, black-body radiation), with AQA GCSE Physics 8463 used as the example specification.