Materials Included In Kit

Additional Materials Required

Prelab Preparation

1. Prepare individual iron-filing trays for each group by adding approximately 5 g of iron filings to each weighing dish.
2. Use scissors or wire cutters to cut the copper wire into eight 1½" long strips.
3. Use scissors to cut the aluminum foil sheet into 4" x 4" square pieces.

Safety Precautions

The materials in this lab are relatively safe. Iron filings can be messy, and it is important to neatly collect the iron filings and place them back into the container after the experiment. Wear safety glasses when performing this laboratory. Wash hands thoroughly before leaving the laboratory. Please review current Safety Data Sheets for additional safety, handling and disposal information.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. The iron filings should be collected and saved in the original bottle for future use. To dispose of the iron filings, follow Flinn Recommended Disposal Method #26a.

Teacher Tips

• Enough materials are provided in this kit for 16 students working in pairs or for 8 groups of students. All materials are reusable. This laboratory activity can reasonably be completed in one 50-minute class period.
• Thorough explanations of magnets and magnetic fields can be found in any physics or physical science textbook. The Background information provided is only a brief description.
• This is an inquiry-based lab. It may be best to perform this lab before magnets and magnetism have been covered in detail in class.
• If the magnetic field of the magnet is too strong, making it difficult to observe the many different magnetic field lines, the magnetic field can be weakened by placing a thicker piece of cardboard between the magnets and the index cards. For each group, cut a 3" x 5" piece of cardboard from a shipping box or from the back of a paper note pad, if necessary. Place this thicker cardboard on the magnets and then place the index cards on top of the cardboard.
• A pinch technique can be used to sprinkle the iron filings in a more controlled manner. Pinch the iron filings between the thumb and index finger and then sprinkle them evenly on the index card. However, the iron filings will leave a metal dust smudge on fingers that is easily transferred to clothing or other objects. Make sure students are aware of this stain before suggesting this technique, and that they thoroughly wash their hands after completing this portion of the experiment.

Sample Data

Observations

North pole/north pole interactions: The two ends do not want to touch. The magnets repel each other. The magnets feel like they want to rotate away from each other.

South pole/south pole interactions: Similar inter action to the north pole/north pole coming together. The two ends do not want to touch. The magnets repel each other. The magnets feel like they want to rotate away from each other.

North pole/south pole interactions: The magnets are pulled towards each other. When the two ends touch, they “stick” together. It takes some effort to pull them apart.

Magnetic Fields

Fill in each circle to indicate the direction of the red tip of the compass needle as the compass is moved around the magnet.

Draw the magnetic field lines of a single permanent magnet. Draw the magnetic field lines of the two magnets with north and south poles facing each other. Draw the magnetic field lines of the two magnets with either north or south poles facing each other. Magnetic Properties of Different Materials (put a check in the appropriate column):

Answers to Questions

1. Describe what happens when two identical poles of the bar magnet face each other. What happens when two opposite poles face each other?

   When two bar magnets are brought close together with their north poles (or south poles) facing each other, the magnets repel each other. The two magnets do not want to touch. When the north pole of one magnet is brought close to the south pole of another magnet, the ends are attracted to each other and the magnets come together. Once together, the magnets are difficult to separate.

2. What polarity must the red tip of the compass needle be since it points towards the south pole of the magnet?

   The red tip must be the north pole of the magnetic needle because north and south poles are attracted to each other, whereas two north poles would repel.

3. Draw a picture to show what would happen if a bar magnet was cut into two equal pieces. Label the north and south poles of each “new” magnet.
   {13913_Answers_Figure_8}
4. How does the direction of the compass needle change as the compass is moved along a magnetic field line?

   The compass needle is always aligned tangent to the magnetic field lines. The only time the needle points at the magnet is when it is near the end of the poles.

5. How do the iron filings align themselves in relation to the magnetic field? Do the magnetic field lines ever cross?

   The iron filings align similarly to how the compass needle pointed in the different regions. They are aligned tangent to the magnetic field lines, and only point toward the magnet near the poles. The magnetic field lines never cross each other. Each one makes its own loop from north pole to south pole.

6. Where is the magnetic field the strongest? How can you tell? Compare the strength of the magnetic field to the closeness of the magnetic field lines.

   The magnetic field is the strongest at the poles, both north and south. The force field strength is felt when the magnets are pulled toward each other, or pushed away from each other. The force is felt the most when the magnets’ poles are positioned close to each other. The magnetic field lines are more closely spaced near the poles compared to the middle of the magnet or far away from the magnet poles. Therefore, the stronger the magnetic field, the closer the magnetic field lines are (more lines per unit area) in that region.

7. Is a typical refrigerator door made of iron or aluminum? Explain.

   A refrigerator door is most likely made of iron because iron can be magnetized. Aluminum cannot be magnetized so a refrigerator magnet would not “stick” to a refrigerator with an aluminum door.

Introduction

Permanent magnets can be found “sticking” to almost every refrigerator in America. They are used to hold up pictures, calendars, coupons, artwork, and test papers with good grades, among other things. Why do magnets “stick” to the refrigerator? In this lab activity, learn about the properties of permanent magnets and their magnetic fields.

Concepts

• Permanent magnets
• Magnetic poles
• Magnetic fields
• Magnetic materials

Background

Why are some materials magnetized and others not? It has been known since ancient times that a mineral known as lodestone exhibited a strange attractiveness 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 magnetism was still a mystery up until a few hundred years ago. Scientists first determined that a material’s ability to become a magnet was based on its chemical composition. After the discovery of the electron, 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, these tiny magnets are balanced so there is no net magnetic effect. Simply stated, in non-magnetic materials, for every tiny magnetic electron that points up, there is a tiny magnetic electron that points down, so that there is no “excess” magnetism pointing in any direction. In materials such as lodestone, there is unbalanced magnetism. It was many years after the discovery of lodestones that their composition was determined to be iron ore. Why does iron have the property of magnetism? It was discovered that atoms of iron, along with those of cobalt and nickel, possess excess magnetic electrons that are not balanced by other magnetic electrons. Since there is unbalanced magnetism in these atoms, they have the potential to become magnetic—they are magnetically susceptible.

In order for a magnetically susceptible substance to actually become magnetic, the excess magnetic electrons must point so that the magnetism “points” in the same direction. Normally, these excess, unbalanced magnetic electrons point in random directions, so the materials are not magnetic (see Figure 1). However, in the presence of an external magnetic field, iron, cobalt and nickel can become induced magnets. A magnetic field is the region around a magnet in which a magnetic force can be felt by other magnetic materials. The strength of the magnetic force field is not constant, but varies with distance from the magnetic poles of the magnet. When a magnetically susceptible object such as iron is placed in a magnetic field, the excess magnetic electrons will align themselves with the external magnetic field, therefore inducing the material to become magnetic. When the external magnetic field is removed, the excess magnetic electrons will again point in random directions and the material will lose its magnetic property. In order to form a permanent magnet, a magnetically susceptible material must be formed or processed in a special way so that the excess magnetic electrons are “locked” into one direction and do not become randomly orientated over time. The iron in lodestones became permanently magnetic because the molten iron cooled and hardened while surrounded by the magnetic field of the Earth.

An important property of a magnet is that all magnets have two opposite-polarity poles, a north pole and south pole. In fact, there has never been any conclusive evidence of a single-poled magnet, or monopole. No matter how small a bar magnet is broken up, each piece will always have a north pole and a south pole. The purpose of this activity is to study the attractive properties of the north and south poles of a bar magnet and observe the shape and properties of the magnetic field that surrounds a bar magnet.

Materials

Safety Precautions

The materials in this lab are relatively safe. Iron filings can be messy and it is important to neatly collect the iron filings and place them back into the container after the experiment. Wear safety glasses when performing this laboratory. Wash hands thoroughly before leaving the laboratory.

Procedure

Observations

1. Obtain two bar magnets, a compass and a piece of chalk.
2. Bring the compass near, but not touching, one of the bar magnets. Notice how the compass needle moves as it gets close to the magnet.
3. With a piece of chalk, mark the end of the magnet that attracts the red tip of the compass needle. This is the south pole of the magnet.
4. Repeat step 3 for the other magnet.
5. Bring the two magnets together so their south (marked) ends face each other. How do the magnets interact? Record your observations in the worksheet.
6. Rotate each magnet 180 degrees and bring the north ends of the magnets together. How do the magnets interact? Record your observations in the worksheet.
7. Rotate one magnet 180 degrees and keep the other magnet the same direction.
8. Bring the magnets together again with the north and south ends facing each other. How do the magnets interact? Record your observations in the worksheet.

Magnetic Fields

9. Place one magnet flat on the table.
10. Following the diagram on the worksheet, record the direction the red tip of the compass needle points as the compass is moved around the magnet. When finished, move the compass away from the magnetic field of the bar magnet.
11. Obtain two index cards, 5 g of iron filings in a weighing dish and both bar magnets.
12. Lay one bar magnet flat on the table and place the index card over the magnet (see Figure 2).
    {13913_Procedure_Figure_2}
13. Carefully sprinkle the iron filings on the index card. Sprinkle a small amount of iron filings to cover the entire card at first. Then, add more iron filings where lines appear to form. Observe the lines that form as the iron filings line up with the magnetic field of the magnet. Draw the magnetic field lines produced by one magnet in the worksheet.
14. Carefully lift the index card off the magnet, keeping the card horizontal to prevent spilling the iron filings. Note: Do not allow the iron filings to contact the bar magnet directly. The iron filings will be difficult to remove once they “stick.”
15. Neatly pour the iron filings back into the weighing dish.
16. Obtain the second bar magnetic.
17. Line the two magnets up, north pole to south pole, about 2 cm apart as shown in Figure 3. Transparent tape can be used to secure them to the table if necessary.
    {13913_Procedure_Figure_3}
18. Place two index cards over the magnets so that the index cards overlap (see Figure 3).
19. Carefully sprinkle the iron filings on the index cards. Sprinkle a small amount of iron filings to cover the entire card at first. Then, add more iron filings where lines appear to form. Observe the lines that form as the iron filings line up with the magnetic field of the magnets. Draw the magnetic field lines in the worksheet.
20. Carefully lift the index cards off the magnets, keeping them horizontal to prevent spilling the iron filings. Note: Do not allow the iron filings to contact the bar magnet directly. The iron filings will be difficult to remove once they “stick.”
21. Neatly pour the iron filings back into the weighing dish.
22. Rotate one of the magnets 180 degrees so that the both north poles or both south poles are facing each other. Space them about 2 cm apart. Transparent tape can be used to secure them to the table if necessary.
23. Repeat steps 18–21.

Magnetic Properties of Different Materials

24. Obtain the aluminum foil, iron nail, plastic straw, copper wire and a bar magnet.
25. Which material is attracted to the magnet, and therefore magnetic? Record your observations in the worksheet.
26. The iron filings should be collected and saved according to your teacher’s instructions.

Student Worksheet PDF

13913_Student1.pdf