A periscope is a simple tool that lets you see over, around, or past an obstacle without moving your head into view. You can build one for a school project using a cardboard box or tube, two small flat mirrors, tape, scissors, and a ruler. The project matters because it shows how light travels and reflects in a way you can test with your own eyes.
It also connects classroom science to real tools used in submarines, forts, and observation devices.
The main idea is that light travels in straight lines until it hits a surface, such as a mirror. In a basic periscope, two mirrors are placed at 45 degree angles so light from the top opening bounces down the tube and then bounces into your eye at the bottom opening. The two reflections keep the image upright if the mirrors are lined up correctly.
Careful measuring, neat cutting, and correct mirror angles make the periscope work much better.
Key Facts
- Light travels in straight lines through air unless it is reflected, refracted, or blocked.
- Law of reflection: angle of incidence = angle of reflection.
- A basic periscope uses two flat mirrors placed at 45 degrees to the tube.
- Two reflections in a simple periscope usually make the image appear upright.
- A larger mirror can collect more light, making the view brighter.
- Periscope height can be estimated by total length = distance between the two mirror centers.
Vocabulary
- Periscope
- A device that uses mirrors or prisms to let a person see from a different position, such as over an obstacle.
- Reflection
- Reflection is the bouncing of light off a surface.
- Mirror
- A mirror is a smooth surface that reflects light in a regular way to form an image.
- Angle of incidence
- The angle of incidence is the angle between an incoming light ray and an imaginary line perpendicular to the surface.
- Angle of reflection
- The angle of reflection is the angle between a reflected light ray and an imaginary line perpendicular to the surface.
Common Mistakes to Avoid
- Putting the mirrors flat against the box wall is wrong because the light will not bounce from the top opening down to the bottom opening.
- Using mirrors at different angles is wrong because the light path may miss the second mirror or enter your eye at the wrong direction.
- Cutting openings that do not line up with the mirrors is wrong because light needs a clear path into and out of the periscope.
- Using wrinkled foil instead of a flat mirror is wrong because uneven surfaces scatter light and make the image blurry.
Practice Questions
- 1 A cardboard periscope is 40 cm tall, and the top and bottom mirrors are centered 5 cm from each end. What is the distance between the centers of the two mirrors?
- 2 A light ray hits a flat mirror in the periscope with an angle of incidence of 35 degrees. What is the angle of reflection?
- 3 Explain why a periscope needs two mirrors instead of only one if you want to look through a lower opening and see an object above a wall.