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.
Understanding Make a Periscope
The important part of a periscope is not just having two mirrors. The mirrors must face the right way relative to each other. Each reflective surface needs to send the light toward the next place it must go.
If one mirror is turned slightly, the light can hit the cardboard wall instead of reaching the second mirror. This is why a periscope may show only darkness or a narrow strip of the scene even when the openings look clear.
Before taping anything permanently, hold each mirror in place and test the view. Small changes in position can make a large difference.
Mirror size affects how easy the periscope is to use. A small mirror accepts light from a smaller part of the scene, so the viewing area can feel like looking through a tiny window. A larger mirror gives a wider, brighter view, but it must still fit neatly inside the tube.
The openings should be cut to match the useful area of each mirror. An opening that is much larger does not improve the view if the mirror behind it is small. Dark cardboard inside the tube can reduce unwanted reflections from shiny surfaces, which may otherwise make the image look washed out.
A good build depends on keeping the tube straight and the mirrors secure. A bent cardboard box can shift the mirror positions, causing the top and bottom light paths to miss each other. Measure from the center of one mirror to the center of the other when comparing different designs.
A longer tube raises the viewing point higher, though it can become harder to hold steady. Strong tape is useful, but tape placed across the reflecting face will block light and spoil the image.
Plastic mirror sheets can work, yet thin sheets may bend and produce a distorted view. Flat glass mirrors usually give a sharper image, though their edges need careful handling.
This project is a useful way to practise fair testing. Change only one feature at a time, such as the mirror angle, tube length, or opening size. Then record what happens to brightness, image position, and the amount of scene visible.
Test the periscope in a well lit room and near a window, since brighter objects send more light toward the top mirror. Notice that the device does not create light or allow sight through solid objects. It redirects light that already comes from the object.
Similar ideas appear in car mirrors, camera viewfinders, security mirrors, and optical instruments. Learning to trace the path of light carefully helps students explain why each part of the model is needed.
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.