Spy gadgets - look through a keyhole

Spy gadgets - look through a keyhole

Be a top secret spy

You can make a spy glass that lets you look through keyholes!

What you need:

  • Clear glass marble
  • Sellotape
  • Ruler
  • Scissors
  • Pencils
  • Black paper or thin card

How to:

Ask an adult for help using scissors

  1. Cut the paper so that it measures 20cm x 8cm.
  2. Roll the paper tightly around your marble.
  3. Sellotape along the edge of the paper so that it stays in position.
  4. Use the pencil to poke the marble to one end of the paper so that it sticks out a bit.
  5. Place the marble against a keyhole and look through. What can you see?

To see a picture of the spyglass go to education.com.

What's happening?

The marble helps you to see through the keyhole! It acts as a "fisheye" lens. The shape of the marble distorts the light coming towards you, so the image might look slightly stretched.

Does everything look upside down? Because the marble is curved, the light has to travel through two convex lenses. This causes the light to be flipped upside down.

Curriculum information