Materials Included In Kit

Additional Materials Required

Prelab Preparation

1. Make a cardboard platform for each group by using pushpins to attach a size 5 cork stopper to each of the four corners of the 5½" x 8½" sheets of cardboard. The narrow end of the stopper should be against the cardboard (see Figure 5). (Optional) Apply a small amount of glue to the narrow end of the stopper before inserting the pushpin to prevent the stoppers from coming loose with handling.
   {12760_Preparation_Figure_5}
2. Remove one sheet of photosensitive paper from the package and the inner black bag. Be careful not to expose the paper to sunlight. Cut the sheet in half to make two 3½" x 5" sheets. Return the half-sheets to the black bag. Repeat with the other sheets until you have the desired quantity.

Safety Precautions

The materials in this activity are considered safe. Handle the magnets carefully; they may break if dropped. Iron filings can be messy; do not handle the filings with bare hands. Do not allow the magnets to come in direct contact with the iron filings. It is important to neatly collect the iron filings and place them back into the container after the activity. Ultraviolet rays are damaging to the eyes. Never look directly into the UV light or Sun. Wear safety glasses. Wear chemical resistant gloves or use tongs while rinsing the photosensitive paper. Remind students to wash their hands thoroughly with soap and water before leaving the laboratory.

Disposal

The developed magnetic field prints can be saved and attached to the students’ worksheets or displayed in the classroom. They may also be disposed of in the regular trash.

Lab Hints

• Enough materials are provided in this kit for 8 groups of students. A total of 30 prints may be made. This laboratory activity can reasonably be completed in one 45- to 50-minute class period. The Prelab Questions may be completed before coming to lab, and the Post-Lab Questions may be completed the day after the lab.
• If time permits, students may assemble their own cardboard platforms.
• This activity should be completed on a sunny or near sunny day. Ultraviolet light is required to expose the photosensitive paper. In bright sun, an exposure time of 2 minutes is sufficient. Three to four minutes may be required if the sky is partly cloudy. Do not overexpose the paper beyond a pale blue.
• An ultraviolet lamp, available from Flinn Scientific (Catalog No. AP9030) is a good indoor alternative for exposing the photosensitive paper. A 3- to 4-minute exposure time is sufficient when the lamp is placed 6 inches above the cardboard platform.
• Keep the photosensitive paper in the black bag until just prior to use.
• Even though most indoor lighting will not expose the photosensitive paper, it is best to keep classroom light to a minimum during the setup phase of this activity. Do not complete the setup phase in sunlight.
• Pans of tap water may be used instead of running water to process the photosensitive paper. Immerse the sheets of paper in the water for 1 minute.
• For ease of collection of stray iron filings, students may place the magnet in the corner of a small plastic bag and sweep the bag across the bottom of the shoebox and work area. The bag is then positioned over the container of iron filings. The magnet is slowly pulled out of the bag while the bag is pushed down. The filings will drop into the container.

Teacher Tips

• The beautiful artwork produced makes this a great integrated activity to introduce a study of magnetism. Students may refer to their permanent prints throughout the unit.
• Two groups may make a print together using two magnets. Some groups may make a print showing opposite poles facing each other and others showing like poles facing each other.
• Try other magnet shapes (e.g., horseshoe, ring, U-shape, disc).
• Students should observe the filings aligning vertically (standing up) directly above the poles of the magnet. This shows the three-dimensional aspect of a magnetic field. Help students understand that the filings do not form a loop in space over the magnet because the magnetic force away from the magnet is weaker than the gravitational force acting on the filings.
• The Flinn Student Laboratory Kit, Introduction to Magnets (Catalog No. AP6457) and the Flinn Activity Stations Kit, Magnets and Magnetism (Catalog No. AP7013), may be used to further explore magnetism.

Answers to Prelab Questions

1. Using the concept of magnetic domains, explain why some materials can be magnetized and others cannot.

   The magnetic force of electrons in most materials is balanced, so these materials do not have magnetic domains and cannot be magnetized. The electrons in ferromagnetic materials are not balanced, creating magnetic domains that can be aligned, resulting in a net magnetic force.

2. A steel paper clip containing iron is brought within the magnetic field of a permanent magnet. Which illustration from Figure 1—a, b or c—would represent the magnetic domains of the paper clip? Explain.

   The magnetic domains of the paper clip would be represented by Figure 1b. While the paper clip is within the magnetic field the domains would be somewhat aligned, forming a temporary magnet.

3. What precautions should be taken when using magnets and iron filings?

   Handle the magnet carefully; it may break if dropped. Iron filings can be messy; do not handle the filings with bare hands. Do not allow the magnet to come in direct contact with the iron filings. It is important to neatly collect the iron filings and place them back into the container after the activity.

Sample Data

The filings align end to end to form lines that go from one pole across the magnet to the other. The lines also radiate out from the poles in arcs, looping from one pole to the other. The lines appear in bands with blank spaces in between. At the poles the filings form vertical lines projecting away from the paper (similar to Figure 2).

Answers to Questions

1. Observe the developed print of the magnetic field. How can you tell where the magnet was positioned?

   The lines of magnetic force radiate outward from the poles of the magnet. The lines converge in two places indicating the ends of the bar magnet.

2. What can you conclude about the strength of the magnetic field in relation to the distance from the magnet? What evidence supports your conclusion?

   The lines of force become less distinct as the distance from the magnet increases because the filings are more random in orientation. This indicates the magnetic force becomes weaker as the distance from the magnet increases.

3. The lines of force appear as small dots on the area of the developed paper that was directly over the poles. Consider your observations from step 13 of the Procedure and explain why this is so.

   The filings formed vertical lines directly over the poles indicating the strongest area of the magnetic field. These vertical lines appear as small points after the photosensitive paper is exposed and developed.

4. Which illustration from Figure 1 of the Background section—a, b or c—represents the magnetic domains of the iron filings after they are sprinkled on the photosensitive paper? Which one represents the magnetic domains of the filings after they are returned to the container? Explain your answers.

   When the filings are in the magnetic field of the permanent magnet, each becomes a temporary magnet represented by Figure 1b. Figure 1a represents the filings after they are returned to the container. Once removed from the magnetic field, the domains become randomly oriented again.

References

Special thanks to Stephen Fuller, Lincoln College Prep High School, Kansas City, MO, for sharing this activity with Flinn Scientific.

Electricity and Magnetism. HyperPhysics. http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/elemag.html (accessed June 2008).

Introduction

A magnet exerts an invisible force on certain objects. The area of force around a magnet, the magnetic field, is often depicted by lines extending from one pole of the magnet to another. These “lines of force” can be seen by using iron filings, and with the help of special paper, a permanent print of a magnetic field can be made.

Concepts

• Ferromagnetic material
• Magnetic field
• Magnetic domains
• Magnetic poles

Background

Since ancient times it has been observed that a mineral known as lodestone exhibited a strange attractive force toward other materials containing this mineral. This attractive property was called magnetism. Although many scientists studied magnetism over the centuries, the origin and cause of this force was still a mystery until more recent history. After the discovery of the electron in 1897 by J. J. Thomson (1856–1940), it was verified that the interaction of the electrons in the atoms determines whether a material can be magnetic.

Every electron spinning around the nucleus of an atom acts like a tiny magnet. In most materials, the forces of these tiny magnets are balanced so there is no net magnetic effect. In ferromagnetic materials such as iron, nickel, and cobalt, the atoms possess electrons that are not balanced by other electrons. Normally, groups of these unbalanced electrons, known as magnetic domains, point in random directions. In this case the magnetic forces of the domains cancel each other out and the material is not magnetized (see Figure 1a). However, in the presence of a magnetic force such as the magnetic field around a permanent magnet, the magnetic domains of a ferromagnetic material begin to align with the magnet’s lines of force. The material becomes a temporary magnet (see Figure 1b). When the external magnetic field is removed, the magnetic domains will again point in random directions and the material will lose its magnetic property. In order to form a permanent magnet, a ferromagnetic material must be formed or processed in such a way so that the magnetic domains are aligned and “locked” in one direction and do not become randomly oriented over time (see Figure 1c).

The strength of a magnetic field is not constant, but varies with distance from the magnetic poles of the magnet. Each magnet has two poles, a north pole and a south pole, so named because if allowed to move freely, the north pole of a magnet will point toward the Earth’s North Pole. The magnetic lines of force travel from the north pole of a magnet to the south pole. The magnetic field does not stop at the poles, however, it continues through the magnet, forming a continuous loop (see Figure 2). If a magnet is broken into two pieces, a continuous loop forms around each piece, so each piece becomes a separate magnet with north and south poles.

Experiment Overview

The purpose of this activity is to make a permanent print of the magnetic field of a magnet using iron filings and photosensitive paper. The patterns of the magnetic force will be observed and conclusions made.

Materials

Prelab Questions

1. Using the concept of magnetic domains, explain why some materials can be magnetized and others cannot.
2. A steel paper clip containing iron is brought within the magnetic field of a permanent magnet. Which illustration from Figure 1—a, b or c—would represent the magnetic domains of the paper clip? Explain.
3. What precautions should be taken when using magnets and iron filings?

Safety Precautions

The materials in this activity are considered safe. Handle the magnet carefully; it may break if dropped. Iron filings can be messy; do not handle the filings with bare hands. Do not allow the magnet to come in direct contact with the iron filings. It is important to neatly collect the iron filings and place them back into the container after the activity. Never look directly into the UV light or Sun. Wear safety glasses. Wear chemical resistant gloves or use tongs while rinsing the photosensitive paper. Wash hands thoroughly with soap and water before leaving the laboratory. Please follow all laboratory safety guidelines.

Procedure

1. Obtain a 5½" x 8½" cardboard platform, a 1.5" bar magnet and tape.
2. Turn the platform upside down (cork stopper side up) and place the magnet in the center of the cardboard (see Figure 3).
   {12760_Procedure_Figure_3}
3. Tape the magnet securely in place. Turn the platform right side up and check to make sure the magnet is flush against the cardboard. If not, tape the magnet more securely.
4. Set the platform right side up so it rests on the cork stoppers.
5. Place a weighing dish on the balance and zero the balance.
6. Weigh 2.5 g of iron filings in the weighing dish. Set the dish of filings aside for step 11.
7. Obtain a 3½" x 5" sheet of photosensitive paper.
8. Center the paper, blue side up, on the platform. Note: The position of the magnet under the platform should be in the center of the paper on top of the platform.
9. Tape the corners of the photosensitive paper in place with small pieces of tape. The portion of tape on the paper should be kept to a minimum (see Figure 4).
   {12760_Procedure_Figure_4}
10. Place the platform with the photosensitive paper in a shoe box.
11. Carefully shake the dish of iron filings over the photosensitive paper. DO NOT “DUMP” THE FILINGS ONTO THE PAPER. The filings should be evenly sprinkled over the entire area of the photosensitive paper first. Sprinkle more filings where lines appear to form.
12. Carefully lift the shoe box and gently tap the box on the table several times. This will help the iron filings align with the magnetic field of the magnet.
13. Closely observe the pattern made by the iron filings. Look at the filings at eye level also. Record your observations in detail on the Make a Print of a Magnetic Field Worksheet. Include a description of the orientation of the filings as well as the pattern they form in relation to the magnet.
14. Place the lid on the shoebox and carry the box outside to a sunny location. Be careful to keep the box level and steady. (Optional) The instructor may have you place the box under an ultraviolet lamp in the laboratory instead of going outside.
15. Place the box on a level surface.
16. Remove the lid, allowing sunlight to fall on the photosensitive paper.
17. Expose the photosensitive paper to full sunlight until the paper is a very pale blue, approximately 2 minutes. Note: If the sky is somewhat overcast, a longer exposure time of 3 to 4 minutes may be necessary. Do not overexpose the paper beyond a pale blue.
18. Replace the lid on the shoe box and return to the classroom.
19. Slowly peel the tape from the platform and photosensitive paper.
20. Carefully lift the paper from the platform, curl the paper slightly to gather the filings in the center, and pour the iron filings back into the weighing dish.
21. Wearing gloves or using tongs, rinse the photosensitive paper under tap water for 1 minute.
22. Lay the paper flat on a paper towel to dry, exposed side up. Carefully blot excess water from the top of the photosensitive paper with a paper towel.
23. Observe the white patterns on the paper. Check the white patterns the next day. They will be more distinct as the blue portion of the paper will darken over time.
24. Attach the developed print to the Make a Print of a Magnetic Field Worksheet.

Student Worksheet PDF

12760_Student1.pdf