Converging lens ray diagram simulation

Ray diagrams are one of the most-practised skills in school optics. This optical bench draws them for you, live: move the object or change the focal length and the rays, the image and the numbers all update.

Interactive, free and runs in your browser. Part of the Optics simulations.

What you will see

An amber object arrow stands on a bench in front of a converging lens. Three principal rays leave its tip: parallel to the axis then through the far focal point, straight through the centre, and through the near focal point then parallel. They meet at the cyan image. Inside the focal length the rays diverge and dashed lines trace them back to a virtual, upright, magnified image.

Try this

  1. Put the object at 2f and confirm the image is at 2f, the same size and inverted.
  2. Move the object to f and watch the image run off to infinity.
  3. Move it inside f to make a magnifying glass.

Common misconception

You do not need all three principal rays to find an image: any two locate it. And a virtual image is not imaginary; you can see it by looking through the lens, but you cannot project it onto a screen.

Exam-style question

An object is 15 cm from a converging lens of focal length 10 cm. Where is the image and what is the magnification?

1/v = 1/f − 1/u = 1/10 − 1/15 = 1/30, so v = 30 cm on the far side. m = −v/u = −30/15 = −2: a real, inverted image twice the size.

Key equations

  • 1/f = 1/u + 1/v
  • m = −v / u
  • P = 1 / f

Curriculum

AQA A-level physics 3.3.2, IB Physics C.2 and C.3.

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