Make Your Own Periscope!

An understanding of optics begins with exploring and enjoying the fun and tricks of light. In this activity, make a simple periscope that will let you see around corners and over walls.

• Two empty milk cartons

• Cardboard cutter

• Gaffa tape

• Pencil

• Two rectangular hand mirrors

• Ruler

• Scissors

• To create a simple instrument for observation

• Have fun with optics

• Build model-making skills

Why can we see objects? How do we see the road, or our friends, or the moon? The answer is: light. The bottom line is that without light, there would be no sight. We are able to see because light from an object can move through space and reach our eyes. Once light reaches our eyes, signals are sent to our brain, and our brain deciphers the information in order to detect the appearance, location and movement of the objects we are observing. The whole process would not be possible if it were not for the presence of light.

All objects that we see can be placed into one of two categories: luminous objects and illuminated objects. Luminous objects are objects that generate their own light. Illuminated objects are objects that are capable of reflecting light to our eyes. The Sun is an example of a luminous object, while the moon is an illuminated object.

Light travels in a straight line and mirrors reflect it. When a light ray hits an object and bounces off, it is called reflection. Mirrors are very good at reflecting, they reflect most of the light that hits them. By placing mirrors in the right way we can also deflect light, and send it in a specific direction. This allows us to look around corners or over obstacles without being seen. As with all models, making this periscope, and experimenting with it, is the best way to understand how it works.

Playing with mirrors, reflections, and light is great fun! 

CAUTION: Sharp tools! Ask an adult to do all the cutting.

Step 1

After making sure that your two empty milk cartons are clean and dry, cut off their tops. (Image 1)

Step 2

Using a cardboard cutter, ask a grown-up to make a window at the base of one carton. (Image 2)

Step 3

This is your viewing window. (Image 3)

Step 4

Lay the carton on its side so that the window is facing the right. Draw a line 45˚ from the bottom right-hand corner to where it meets the left hand edge. (Image 4)

Step 5

Flip the carton over so that the window is now facing the left and draw a line 45˚ from the bottom left-hand corner to where it meets the right-hand edge. (Image 5)

Step 6

Make a cut on that line ONLY as long as the shorter side of the hand mirror. (Image 6)

Step 7

Flip the box over and do the same on the other diagonal line. (Image 7)

Step 8

Insert the mirror into the slot (if the cut is too narrow, widen the cut to fit the mirror). The reflecting side must face the window. (Image 8)

Step 9

Hold the carton up and look through the window. Ask your partner to wiggle their fingers over the top. If what you see is tilted or distorted, adjust your mirror until it straightens out. If the mirror is loose, tape it in place. (Image 9)

Step 10

When you are satisfied with one carton, follow exactly the same steps with the second one. You will finish with two identical cartons, each with a mirror set in the base at a 45˚angle. (Image 10)

Step 11

Place one carton on the table with the window facing you. Place the other carton on top with the window facing away from you. Pinch the top carton a little so that it slips just inside the bottom carton. Tape them securely. (Image 11)

Step 12

Get ready to watch from a concealed spot. (Image 12)

Step 13

Hold it sideways to see around corners. (Images 13–14)

Step 14

You can also look through the bottom window and see over fences. Look through the top window and see under tables. Experiment with a longer tube and notice that the image gets smaller.