The lens of invisibility

Hide in plain sight!

Difficulty:
Danger:
Duration:
15 minutes
The lens of invisibility

Safety

  • You will use a safe Class 1 laser in the experiment. It is perfectly safe when used as outlined in the instructions.
  • Do not aim laser beam at eyes or face.
  • Never leave lenses exposed to direct sunlight; this is a fire hazard.
  • Read the "Working with Batteries" section of the safety guidelines carefully before proceeding. Always disconnect the setup after finishing the experiment.

Step-by-step instructions

Round transparent objects that change the direction of light beams are called lenses. A set card is a lens made up of many small cylindrical lenses. Observe on the screen how they change the direction of the beam.

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You have verified that the lenticular lens changes the direction of the laser beam like a cylindrical lens. The change in the direction of the rays passing through the lens leads to unusual visual effects—check them out using crossed popsicle sticks.

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Can a lenticular lens change a picture’s colors?

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Disposal

  • Dispose of solid waste together with household garbage.
  • Dispose of used batteries in accordance with local regulations.

Scientific description

Transparent objects that have a rounded side and can change the directions of light rays are called lenses. They can have various shapes. The glass in the first experiment had a cylindrical form , so it’s a cylindrical lens. You’ve seen how it changed a laser beam . The transparent plate  from the kit is also a lens, consisting of a large number of small cylindrical lenses .

When you look at the picture through the plate, the rays reflected from it pass through the plate  and, on each small lens , form small copies of the whole picture the size of the lens. Many small, elongated squares are formed on the lens very close to each other; however, our eyes cannot distinguish them, so it seems that the squares  from the same line merge into a strip .

How does this lens make the popsicle stick  disappear? When the stick  and lens  are located so the vertical popsicle stick is replicated in all small lenses , the replicas are so small that our eyes cannot distinguish them. This makes the popsicle stick invisible to us. If you rotate the popsicle stick, the horizontal stick will be replicated, and our eyes can distinguish those replicas. This renders the popsicle stick visible! Such a lens is called a lenticular lens.