Cardboard Periscope

What you'll learn

Light travels straight and bounces off a mirror at the same angle it hits — the law of reflection. Two mirrors at 45° let you see over a wall.

What you need

• cardboard box (cereal or shoe box)
• 2 small mirrors (or foil from a baking tray)
• scissors, tape

Steps

Step 1 — Cut the viewing ports

Cut a hole near the top of one end and near the bottom of the other. These are where you look in and where light enters.

Step 2 — Angle the mirrors

Tape each mirror at 45° facing the other. The bottom mirror sends light up to the top one, then to your eye.

Step 3 — Test it

Hold it over a chair or wall. You should see what's on the other side. Paint the inside black if the image is dim.

Try this

• rebuild with a longer tube — does the image get brighter?
• what happens if you tilt one mirror?

Where it's used in the real world

• submarines use periscopes to see above water
• doctors use tiny scopes to look inside the body