Diverging lenses, and glasses for short and long sight sim
Find the virtual focus of a diverging lens with a ray box by marking crosses and ruling lines, draw its ray diagram and measure the virtual image, then give a short-sighted and a long-sighted model eye the trial lens that makes its retina picture sharp.
Light: thin lenses, diverging lenses and correcting sight · covers the IGCSE, GCSE topic
What the sim shows
Model. Thin lenses, traced ray by ray (paraxial): a lens of focal length f (negative for a diverging lens) turns a ray at height y by −y/f. Station A: five parallel rays 12 mm apart through a Perspex lens shape (f = +10 cm, −15 cm, or an unknown diverging one); your crosses and lines find F. Station B: a full-size ray diagram, diverging lens f = 4.0 cm, object 2.0 cm tall. Station C: a model eye six times life size, lens f = 10 cm with a 16 mm iris, retina 15 cm (short sight) or 10 cm (long sight) behind it; glasses 1 cm in front; a window 10 m away or a lamp box 30 cm away. The image on the retina is drawn with the blur the rays give; nothing is snapped sharp. No aberrations. The lens equation is not used on the page.
- The lens shape (stations A and B); the retina screen (station C)
- Ray box, paper, ruler, supply, model eye on its rail, tray of trial lenses
Use it in your lessons
- Try it here: anyone can unlock 2 figures free, and a free account unlocks up to 5. Runs on a laptop, a Chromebook or a phone; nothing to install.
- Present it and share student links with the teacher plan, from US$5 a month, billed yearly.
- Put it on your own website or LMS for US$9, paid once, or every sim from US$29 a month.
Free guide: 12 practicals as sims, and how to run one in a lesson →
Need a version for your exact set-up? Have one made: US$49 a figure in an order of 5.
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