Learn properties of light with DIY Periscope

A captain along with his crew is sailing in a submarine. The submarine is submerged under the water. However at times the captain needs to see what is happening on the surface of the water to check if there is a big ship nearby or what the enemies are doing during the way. As the submarine is under the water, normally this is not possible. But submarines have a special device called “Periscope” which enables the crew of the submarine to see whats happening on the surface of the water.

We will be making a Periscope with cardboard box to understand and experiment with the properties of light. Here is a video of this experiment.

What is a ‘Periscope’?

Periscope is a device that has a set of mirrors and long tubes. Normally without a periscope the captain or the crew of the submarine cannot see what’s happening on the surface of the water.

How does a periscope work – Properties of light?

Periscope illustration
Periscope illustration

Periscope’s working is based on the following basic principles of physics.

  1. Light travels really fast and in straight line.
  2. When light rays hit the surface of an object, they bounce off. This is called reflection. When lights hit the surface of a glass or water they reflect at the same angle as it hit the surface.
Ishaan with do it yourself Periscope
Ishaan with do it yourself Periscope

Why is this an interesting exercise with the kids?

  1. It is interesting to learn how light travels, especially by aligning the cuts on the cardboards and the mirrors in the straight line and at the right angle.
  2. Kids and adults can understand setting up of mirrors at angles so that light reflects correctly.

How to build a periscope at home?

Things needed

1. A Cardboard box that is of a cuboid (rectangle) shape.
2. 2 small mirrors
3. A pair of scissors or cut knife
4. Sticky tape

Procedure

Step 1: Cut 2 holes, of the size of the mirrors, in the cardboard using the cut knife. One hole is the ‘viewport’ place at the bottom edge of one end of the cube. The other hole is supposed to be on the opposite side the cube at the top edge. The following images illustrate the positioning of the holes.

Periscope Step1: Cut holes on the opposite sides and opposite edges of the cardboard box
Periscope Step1: Cut holes on the opposite sides and opposite edges of the cardboard box

 

Ishaan looking through the viewport. The hole shown in this image is at the top edge of the box.
Ishaan looking through the viewport. The hole shown in this image is at the top edge of the box.

 

Ishaan looking through the viewport hole. This cut is the one at the bottom edge of the box.
Ishaan looking through the viewport hole. This cut is the one at the bottom edge of the box.

Step 2: Now place the mirrors inside the box at 45 degrees angle opposite to both the holes using sticky tape. The logic behind this is that the light travels through the hole in the top edge and hits the mirror opposite to this hole. This light now gets reflected to the mirror that is opposite to the hole at the bottom edge. This reflection can be seen through the hole at the bottom edge, which we are call a viewport.

Periscope step2: The mirror placement inside the box to enable light reflection
Periscope step2: The mirror placement inside the box to enable light reflection

 

Periscope step3: Mirrors inside the periscope box
Periscope step2: Mirrors inside the periscope box

Step 3: Now if you view from the viewport you can see the reflection of the objects that are in line to the hole in the top edge.

Tip: Beam a laser light onto one mirror and see how it shows up on the other side.

Watching through periscope
Watching through periscope

This experiment teaches the kids the basics of physics and also gives them an introduction to different properties of light.

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