Photograph of an A3 paper mind map of the tricky topic ‘Optics and ray diagrams’ with three lines leading off to the stumbling blocks ‘drawing ray diagrams’, ‘interpreting ray diagrams’ and ‘calculations used in ray diagrams’. These stumbling blocks are linked to student problem examples such as ‘calculations used in ray diagrams’ which each have lines leading to further details such as ‘Pythagoras and maths words’, and ‘If you can’t interpret, you can’t answer questions using equations’.