Seeing Around Corners

What You Need


Materials for one periscope (from Up Periscope!):

  • Two 1-quart milk cartons
  • Two small pocket mirrors (flat, square ones work best)
  • Utility knife or X-Acto knife (for teacher use only)
  • Ruler
  • Pencil or pen
  • Masking tape
Seeing Around Corners Photo Credit: Science NetLinks


To understand how periscopes extend vision beyond the line of sight.


Students at this level should have their attention called to the use of tools and instruments in science and the use of practical knowledge to solve problems before the actual underlying concepts are understood. They should develop the ability to use increasingly sophisticated tools and techniques and improve their skills in measurement, calculation, and communication. Activities that have students make observations and measurements using instruments such as periscopes and microscopes help reinforce the relationship between technology and science. These activities also give students skill and confidence in using tools in their everyday lives.

In addition to experimenting with technology, students should begin to think and write about how technology helps people. They should be encouraged to consider alternative ways of doing something and to compare the advantages and disadvantages of the various options. (Benchmarks for Science Literacy, p. 45.)

In this lesson, students will explore the concept of line of sight by recording the conditions under which they can and can't see an object. They will then build a periscope and experiment with it to determine how this tool helps them extend their line of sight around corners, over walls, and beyond. This activity is based on instructions and information on the Exploratorium website.


To begin this lesson, ask students if everyone sees things exactly the same way. Have them discuss differences they are aware of such as not being able to see things that are far away (nearsightedness) or close up (farsightedness), or not seeing certain colors (color blindness).

Also ask them where they would go in the classroom if they didn't want you to see them. Answers may include behind you, under a desk, or behind a door or wall.

Have students consider these questions:

  • What tools or instruments help people see better?
  • What do these tools do?

Common answers may include glasses, binoculars, telescopes, and magnifying glasses. Students may indicate that these tools make things seem closer or farther away.


Continue the discussion by asking these questions:

  • At what times or in what situations is it impossible for anyone to see anything?
  • Why is this so?

Answers may include when there is no light and when something is not directly in line with their eyes. Explain to students that when we see an object, we are actually seeing the light it gives off. So when it is dark or when an object is not in line with our eyes, we can't see it. Point out that light travels only in straight lines—it can't bend around corners. That's why we can only see what is in a straight line from our eyes—or in our line of sight.

Have students experiment with line of sight by testing at what locations around the room they can and can't see each other.

Then ask students if they know of any tool that can help them see an object that is out of their line of sight. Some students will probably mention periscopes. If they don't, introduce periscopes at this point.

Then ask these questions:

  • What do you know about periscopes?
  • What are they used for in the real world?

Allow students to discuss their understanding of how periscopes are used in submarines. You might ask if they have heard the expression "Up periscope." Explain that this command is used to request the raising of a submarine's periscope.

Tell students that periscopes bring what is around corners, over walls, and beyond into view. Add that they will now have a chance to make their own periscopes and see how they work.

Have students access the Seeing Around Corners student esheet. Tell students that the esheet will direct them to a website that includes information about periscopes as well as instructions for building one.

Note: Alternate assembly instructions can be found at the Molecular Expressions: Science, Optics & You website.

Have students follow the instructions outlined in Step 1 of the esheet. Students might mention words such as perimeter, microscope, and telescope when brainstorming words that contain the roots peri or scopus. If you wish, have them speculate on the meanings of those words.

As noted in Step 2 and Step 3 of the esheet, have students work in small groups to construct a periscope, following the instructions on the website. (Do not distribute knives or let students do any cutting themselves.)

Note: To save class time, you might want to complete Steps 1 and 2 outlined on the website beforehand and give each group two milk cartons with the lids and viewing holes already cut out. Then you could direct students to Step 3 and read Steps 3–9 with them. You could circulate throughout the room and cut the mirror slits as soon as each group has measured and marked them.

Have students complete Steps 4 and 5 of the esheet. Give them plenty of time to experiment with the periscope, looking at objects around the room (including samples of writing) and standing in the same places they did in the Motivation section.

Once students have experienced what the periscope can do, have them return to the Up Periscope! site and scroll down to "How Does My Periscope Work?" (in the "What’s Going On?" section) and discuss how the periscope works.

To facilitate the discussion, you might want to reproduce the diagram on the chalkboard (or ask a student volunteer to do it). Make sure students understand how the angled mirrors bend light rays and allow them to see objects that are out of the line of sight. Make sure that the information you present is appropriate to your students' knowledge and ability level.


In an effort to assess understanding, have students answer the questions on the Seeing Around Corners student sheet.

Following are sample answers to the assessment questions:

  1. How does a periscope let you see around corners and over and under things?
    (The angled mirrors in the ends of the periscope bend light rays. When you look through a periscope, light coming from objects at right angles to your eye is bent so the object comes into your line of sight.)
  2. How does the periscope affect the size and shape of the objects you see?
    (The periscope doesn't affect the size or shape of objects viewed through it. It only allows you to see objects that are out of your line of sight.)
  3. How could you make a periscope that would let you see behind you? Hint: Look at the diagram of how a periscope works and think about where the light has to enter it.
    (You could tape the two milk cartons together with the holes facing in the same direction.)
  4. What ways could periscopes be used in real life?
    (Answers may include situations in which someone needs to see something that is out of the line of sight, such as underwater in submarines, for security in buildings, or inside the body.)
  5. CHALLENGE QUESTION: Can you read writing through your periscope? Why or why not? Hint: Think about what writing looks like in a mirror.
    (You can read writing with a periscope because it is reflected in two mirrors. The first mirror makes it appear backwards and the second makes it look normal again.)

Discuss students' answers to the questions to make sure they understand how a periscope helps them expand their senses—essentially giving them eyes all over their heads.


This lesson may be supplemented by another Science NetLinks lesson, Color Burst, in which students extend their knowledge of light by exploring the separation of colors in water and other solvents.

This lesson is part of a series of Science NetLinks lessons dealing with optical technology. The other lessons in the series include Magnify It! (K–2), Looking into Space (6–8), and Watch Your Thoughts! Diagnostic Imaging and the Brain (9–12).

To reinforce the practical applications of periscopes, suggest that students research their use in submarines. Excellent information can be found at the following websites:

Did you find this resource helpful?

Lesson Details

Grades Themes Type Project 2061 Benchmarks