Periscope

Introduction

Up periscope! Construct and examine the inner-workings of a simple periscope.

Concepts

• Reflection
• Periscopes

Materials

Safety Precautions

Although this demonstration is considered nonhazardous, please follow normal laboratory safety guidelines.

Disposal

The assembled periscope may be saved and reused for future classes.

Prelab Preparation

Periscope Assembly

1. Obtain the 30-cm piece of PVC pipe and the two PVC elbows.
2. Place one of the PVC elbows on one end of the PVC pipe (see Figure 1).
3. Place the other PVC elbow on the remaining end of the PVC pipe pointing in the opposite direction (see Figure 2). Note: No glue or adhesive is required.
4. Position one of the mirrors over the “opening” of the top elbow (mirror side toward the inside). Use a rubber band to hold the mirror in place. Double the rubber band to ensure a tight fit (see Figure 3).
   {13914_Preparation_Figure_1}
5. Repeat step 4 for the other mirror and the bottom elbow.
6. Tape the transparency sheet with the arrow onto the opening of the top elbow. The arrow should point upwards (see Figure 4 in the Procedure section).

Procedure

1. Use the periscope, as prepared above (see Figure 4), to look at images in the room. View items over an “obstruction” such as a desk or a freestanding bookshelf. The arrow should appear normal and right side up.
   {13914_Preparation_Figure_4}
2. Rotate the top elbow of the periscope clockwise 90° from the forward position (see Figure 5). The arrow will be horizontal and rotated 90°.
3. Rotate the top elbow clockwise an additional 90° (see Figure 6). In this case you will be looking behind yourself. The arrow will now be rotated 180° from the original position and will be inverted.
4. Rotate the top elbow clockwise an additional 90° (270° from the original position) (see Figure 7). The arrow will once again be horizontal but will be reversed from the 90° position in step 2.
5. Rotate the elbow clockwise to the original position. A complete 360° rotation will now have been completed. The arrow will once again appear upright.

Student Worksheet PDF

13914_Teacher1.pdf

Teacher Tips

• This kit contains enough materials to assemble one periscope. The periscope should be saved and used with future classes.
• Extra rubber bands are provided in the case of breakage or weakening of the original rubber bands occurs.
• The periscope may also be used in conjunction with a Video Flex camera and a TV or computer monitor.
• As an extension to this activity, have students construct ray diagrams for each of the periscope rotations.

Discussion

A periscope is an optical device that is used to observe objects from a concealed or protected position. Simple periscopes consist of reflecting mirrors at opposite ends of a tube container, usually parallel and at 45-degree angles to each other. The periscope was invented by Simon Lake in 1902 and perfected by Sir Howard Grubb. Simon Lake was aboard the USS Holland and realized that the submarine had one major flaw—lack of vision. The vessel had to return to the surface and crew members had to look through windows in order to obtain any visual contact. To solve this problem, Simon Lake developed an instrument known as the omniscope. The omniscope was constructed using various prisms and lenses and was the predecessor to the periscope. Sir Howard Grubb, a part owner of a telescope company in Dublin, Ireland, used Lake’s design and developed the first modern periscope which was used in British Royal Navy submarines. This periscope design was commonplace in most submarines and was in operation for over 50 years.

Periscopes are commonly introduced in many textbooks when reflection is being discussed. As the periscope is situated in step one of the procedure, the image will be erect and look normal. When the top elbow is rotated 90°, the image appears horizontal and is rotated at a 90° angle. When the elbow is rotated 180° from the original position, the image will be inverted. In this position, the top and bottom reflected rays simply change places while remaining in the same plane. When the top elbow is rotated to the 270° position, the image is once again rotated 90° but the image will be reversed from the 90° position. The images seen in both the 90° and 270° positions actually involve three dimensions. The reflected rays seen in each of these positions shift from a single plane to another plane that is at right angles to the first (see Figure 8).

References

Flinn Scientific would like to thank Jeff Bracken, science teacher at Westerville North High School in Westerville, Ohio, for bringing this demonstration to our attention.

Amann, G. The Physics Teacher, 1996, 34, 408–409.