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Optical Illusions – Circles from Lines

Simple optical illusions make us think about how our eyes and brains work together. This optical illusion does not require much preparation. It is fun for kids to see how they can create circles from lines.

Optical Illusions – Circles from Lines


  • Index card
  • Pencil
  • Ruler
  • Pin


  1. Using a pencil and a ruler, draw four dark lines on a blank index card, as shown in the image at the bottom of the article.
  2. Insert a long pin in the middle of the card – approximately where the dark dot is shown in the image.
  3. Hold the pin steady and spin the card. What do you see?


You should see two concentric circles.

There is a location on each line which forms the smallest circle while the card is spinning. Because this circle is being traced more frequently while the card is spinning, it appears darker, creating the circles you perceive.

Lines drawn on index card for optical illusions

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