Materials Included In Kit

Additional Materials Required

Prelab Preparation

Experiment 1. Properties of Magnets

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 four 1½" long strips.
3. Use scissors to cut the aluminum foil sheet into 4" x 4" square pieces.

Experiment 2. Build an Electromagnet

1. Measure and cut approximately 75 cm of magnet wire for each group.
2. Cut four 1" x 4" pieces from the sandpaper sheet.

Experiment 3. Electromagnetic Induction

1. Measure and cut eight 2-m lengths of magnet wire, two for each group.
2. Cut four 1" x 4" pieces from the sandpaper sheet.

Experiment 4. Build a DC Motor

1. With wire cutters, cut four 60-cm lengths of magnet wire, and eight 8-cm lengths of copper wire.
2. Cut the 6" x 12" x 1" foam piece into four 3" x 3" foam blocks using scissors or a paper cutter.
3. Cut fresh magnet wire and copper wire for each lab group performing this experiment, or leave the wire cutters, wire and meter stick at the lab station for students to cut their own wire (if this is appropriate for your classroom setting).

Safety Precautions

Most of the materials for this lab are considered 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. Students should wear safety glasses when performing this experiment. Students should be advised to wash hands with soap and water when this experiment is complete. 9-V batteries do not have enough electrical current to be harmful, but small shocks are possible. Do not complete the circuit with the battery for more than ten-second intervals. Since there is very little resistance in the wires, the battery can discharge quickly and become very hot if it is connected for a longer duration. Care should be taken when wrapping and unwrapping the wire. The pointed ends of the wire are hazardous to eyes. Wear safety glasses. Please follow all normal laboratory safety guidelines.

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 materials from each lab should be saved and stored in their original containers for future use. 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.

Lab Hints

Experiment 1. Properties of Magnets

• Enough materials are provided in this kit for four student groups of students to work at the same lab station. 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.
• Remind students to move the compass away from the bar magnet after completing step 10 of Experiment 1.
• 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 may easily transfer 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.

Experiment 2. Build an Electromagnet

• Enough materials are provided in this kit for four student groups of students to work at the same lab station. All materials are reusable. This laboratory activity can reasonably be completed in one 50-minute class period.
• The magnet wire can be reused for additional classes as long as it is unwrapped carefully so that there are no kinks in the wire. When removing the magnet wire from the round form (nail), pull the magnet wire firmly and allow the round object to spin between your fingers as the wire unwraps. This will typically produce relatively straight wire with no kinks. Holding the round object secure while unwrapping the wire generally results in curled wire and can easily produce kinks.
• The magnet wire is insulated with enamel to prevent shocks.

Experiment 3. Electromagnetic Induction

• Enough materials are provided in this kit for four student groups of students to work at the same lab station. All materials are reusable. This laboratory activity can reasonably be completed in one 50-minute class period.
• The magnet wire can be reused for additional classes as long as it is unwrapped carefully so that there are no kinks in the wire. When removing the magnet wire from the round form (plastic containers), pull the magnet wire firmly and allow the round object to spin between your fingers as the wire unwraps. This will typically produce relatively straight wire with no kinks. Holding the round object secure while unwrapping the wire generally results in curled wire and can easily produce kinks.

Experiment 4. Build a DC Motor

• Enough materials are provided in this kit for four groups of students to work at the same lab station. All materials are reusable. This laboratory activity can reasonably be completed in one 50-minute class period. Enough magnet wire is provided to build over 30 different coil armatures (depending on the size and number of coils) so that students can experiment with the armature design.
• If the coil armature is laid flat on a table and the enamel is sanded off one “side” of both axles instead of off the “top,” the motor will still work. However, the ceramic magnets will have to be held to the side of the coil armature, instead of above or below the armature. The coil will not continue to spin if the magnets are held above or below the armature if the axles are sanded this way.
• Students may assemble the motor first with one magnet, then investigate the effect of adding a second magnet.

Teacher Tips

• Set up each lab station accordingly before class. Students should leave the stations as they find them before they move on to the next lab station.
• Before class, prepare copies of the student worksheets for each student. The Background information for each experiment can also be copied at the instructor’s discretion. 

  Experiment 4. Build a DC Motor

• If the motor does not spin continuously:
  • Be sure the straight wires from the coil armature are 180° apart and positioned from the center of the magnet wire coil.
  • Check to make sure the enamel on the axle is completely removed and the copper wire is exposed on only one side so half the “axle rod” is copper and the other half is enameled. Make sure that the copper side and the enameled side are the same for both axle ends. Make sure the coil spins freely on the copper coil loops and that it is balanced and level to the ground.
  • Check to make sure the electrical circuit is closed and the battery has enough power. Connecting the leads closer to the loops in the copper coil posts may help. Also, remove any tarnish or contamination that may be on the copper wire post loops with sandpaper.
  • Manually adjust the position of the magnets by holding the magnets above the coil armature with the north or the south end of the magnets pointing at the coil armature. Adjust the distance and position of the magnets while initiating the spin to the coil armature. Determine the best distance for the magnets. The height of the copper posts above the foam can be adjusted accordingly.
  • Once the motor spins, adjust the position and the polarity of the external magnet and observe how the motor spins.

Sample Data

Experiment 1. Properties of Magnets

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 to the interaction of 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): Experiment 2. Build an Electromagnet
Number of paper clips picked up by the electromagnet (with nail core):

The electromagnet with iron nail picked up six paper clips.

Effect on the compass needle.

The compass needle was affected by the electromagnet at a distance of about 10 cm. As the electromagnet was brought closer to the compass, the needle was more strongly affected. The red tip of the compass needle pointed at the electromagnet.

Number of paper clips picked up by the coil of wire (without nail core):

The coil of wire electromagnet picked up only one paper clip.

Effect on the compass needle:

The coil of wire did not affect the compass until the end of the coil was right up next to the compass. It had a much weaker effect on the compass compared to the iron nail electromagnet.

Experiment 3. Electromagnetic Induction
Observed deflection of the compass needle. What movement produces the strongest deflection?

The compass needle deflected slightly as the magnet was dropped into the container. When the compass slid back and forth through the coils, the compass needle deflected in different directions. It didn’t appear that the speed of the magnet traveling through the coils affected the compass needle as much as when the magnet quickly changed directions. Also, keeping the magnet inside the coil for a few seconds, and then tipping the container so the magnet slid out of the coils, seemed to cause a large deflection in the compass needle. When the magnet was moved in and out of the coil using the rod, the compass needle deflected a large distance. It was most affected when the magnet changed directions rather than when the magnet passed through the coils quickly.

Experiment 4. Build a DC Motor

Observations
It took a little time to adjust the coil armature so it was balanced and spun freely on the copper posts. The motor did not start immediately. After the armature was balanced, it had to be initially spun before it turned on its own. Once it started, the motor ran continuously until it fell off one of the copper posts. Adjusting the height of the posts and the position of the armature helped maintain a stable motor.

The motor ran faster when the magnets were held to the side of the motor rather than below or above the motor. Also, the closer the magnets were to the armature, the faster the most rotated. However, the motor still rotated even when the magnets were four to five centimeters from the armature.

A second armature was made that was half the diameter of the first and about half the number of coils. This armature maintained balance for a longer period of time and rotated a little faster. This motor started spinning much easier than the larger armature and behaved similarly to the first armature.

Answers to Questions

Experiment 1. Properties of Magnets

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 be 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.
   {13457_Answers_Figure_18}
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.

Experiment 2. Build an Electromagnet

1. Compare the strength of the electromagnet with the iron nail core to the one without. Why would an iron core have this effect? The iron nail electromagnet was much stronger than just the plain coil. It is at least six times stronger since the iron core electromagnet picked up six paper clips and the coil picked up only one. The iron core improves the strength of the electromagnet because iron can become magnetic. The current-carrying coils produce a magnetic field which causes the iron core to become a temporary magnet. Both magnetic fields combine to produce a stronger magnet.
2. Draw the direction of the magnetic field surrounding the wire loop.
   {13457_Answers_Figure_19}
3. Draw the magnetic field lines around the electromagnet.
   {13457_Answers_Figure_20}
4. Calculate the magnetic field produced by an electromagnet (solenoid) with 100 loops per centimeter with a current of 1 amp. What is the magnetic field of the same electromagnet with an iron nail core? (μ_o = 4π x 10^–7 T•m/A, magnetic susceptibility, k, of air and iron is about 1 and 200, respectively.)

   B_air = kμ_onI
   = 1 x 4π x 10^–7 T•m/A x 10000 loops/m x 1 amp = 0.013 T
   B_iron = 200 x 0.013 T = 2.5 T

Experiment 3. Electromagnetic Induction

1. The 60-mL jar with the coiled wire and compass inside is a simple galvanometer, or a device that detects very small currents. What property of electric current does this simple galvanometer detect?

   The compass of the galvanometer constructed in this experiment detects the magnetic field that is produced by the current traveling through the wires wrapped around the jar. The coils help to amplify the magnetic field of the weak current produced by the solenoid (just like an electromagnet).

2. The bottle preform with coiled wire and moving magnet is a simple solenoid. When the magnet moves through the solenoid, a current is produced in the coiled wire which is then detected by the galvanometer. Based on your observations, what type of magnet motion produced the most current (the largest deflection of the compass needle)?

   The largest deflection occurred when the magnet was caused to quickly change direction inside the coils. Therefore, the largest change in the magnetic field produces the greatest amount current in the wires. (This is in agreement with Faraday’s law.)

3. As the magnet enters the coil loop from the left, what direction does the induced electric current flow in the wire loop? Indicate the current direction on the figure.
   {13457_Answers_Figure_21}

Experiment 4. Build a DC Motor

1. Explain how the DC motor works.

   See Background information. Student explanations will vary. Accept any reasonable response.

2. What is the purpose of sanding only half the enamel off the ends of the coil armature?

   The sanded enamel creates electrical contact during half the armature rotation and no electrical contact for the second half of the rotation. This allows the coil armature to have either a repulsive force with the external magnet or no force with the external magnet. If there was a repulsive and attractive force on the external magnet, the armature would not spin 360 degrees.

3. How does the external magnet polarity determine the spin direction?

   Reversing the direction of the external magnet reverses the direction of the motor spin.

4. If the coil armature was larger, how would this affect the performance of the motor?

   The performance of the armature would probably be less because the armature would have more mass, making it more difficult to spin. Also, the magnetic field in the center of the loop would not be as strong, or concentrated, resulting in less “spinning force.” Smaller armature coils tended to spin faster.

5. If the coil armature had more windings, how would this affect the performance of the motor?

   More windings would improve the performance of the motor because more coils would increase the magnetic field of the coil and thus increase the “spinning force.”

Introduction

This all-in-one Magnets and Magnetism Kit is designed to provide the opportunity to explore the fundamental properties of magnets. Four hands-on lab stations can be arranged so groups can experiment with different aspects of permanent magnets, electromagnets and the uses of magnetism.

Concepts

• Permanent magnets
• Magnetic fields
• Magnetic poles
• Magnetic materials
• Magnetic properties of current-carrying wires
• Electromagnets
• Electromagnetic induction
• Faraday’s law
• Motor fundamentals
• Electric circuits
• Electromagnetism

Background

Experiment 1. Properties of Magnets
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. No matter how small a bar magnet is broken up, each piece will always have a north pole and a south pole.

Experiment 2. Build an Electromagnet
An important property of a moving charged particle, such as an electron, is that it produces a magnetic field. So when many electrons travel in a conducting wire to produce an electric current, these moving electrons produce a magnetic field that surrounds the wire. Magnetic fields are easily detected using a compass which contains a very lightweight permanent magnet (the compass needle) that pivots freely about its midpoint. Even very weak magnetic fields will cause a compass needle to deflect away from its “natural” direction. The north pole of the compass needle “naturally” points toward the magnetic north pole of the Earth.

When current travels around a wire loop, the magnetic field produced by the current is the strongest at the center of the loop. The direction of the magnetic field produced by a looping current is perpendicular to the face of the loop (see Figure 2). When many current-carrying loops are grouped together in a line, such as with a spring or coil of wire, the current travels in the same direction in all the loops and the magnetic fields produced by all the loops add together. To further enhance the magnetic field produced by a current-carrying coil, a magnetizable object, such as iron, can be placed inside the coils. Iron has natural magnetic domains that are normally in a random orientation, making an isolated piece of iron nonmagnetic. However, when a magnetic field is brought close to iron, the magnetic domains will temporarily align with the external magnetic field and the iron becomes magnetic. That is why bar magnets attract iron nails, but iron nails do not attract each other. Because iron has its own magnetic domains, the magnetic properties of an iron nail inserted into a coil of wire will add to the coil’s magnetic field to pro¬duce a very strong magnet—an electromagnet. The magnetic field generated by an electromagnet (solenoid) is proportional to the number of coils per length of the solenoid multiplied by the electric current traveling through the wires (Equation 1).

B = magnetic field (in Tesla)
k = magnetic susceptibility of core
μ_o = 4π x 10^–7 T•m/A
n = number of loops per unit length
I = electric current (in amps)

To put the strength of an electromagnetic into perspective, the Earth’s natural magnetic field at the surface is approximately 5 x 10^–5 Tesla.

Experiment 3. Electromagnetic Induction
An important property of a moving charged particle, such as an electron, is that it produces a magnetic field. So when many electrons travel in a conducting wire to produce an electric current, these moving electrons produce a magnetic field that surrounds the wire. Magnetic fields are easily detected using a compass which contains a very lightweight permanent magnet (the compass needle) that pivots freely about its midpoint. Even very weak magnetic fields will cause a compass needle to deflect away from its “natural” direction. The north pole of the compass needle “naturally” points toward the magnetic north pole of the Earth.

When current travels around a wire loop, the magnetic field produced by the current is the strongest at the center of the loop. The direction of the magnetic field produced by a looping current is perpendicular to the face of the loop (see Figures 3 and 4). When many current-carrying loops are grouped together in a line, such as with a spring or coil of wire, the current travels in the same direction in all the loops and the magnetic fields produced by all the loops add together. 20%;" data-type="center">{13457_Background_Figure_4} As discussed earlier, a moving charge produces a magnetic field. The reverse is also true—a moving magnet (or changing magnetic field) will induce an electric current in a wire. The strength of the induced current is proportional to the rate of change of the magnetic field. This property is known as Faraday’s law and is a consequence of the law of conservation of energy. Therefore, when a bar magnet is dropped through a coil of copper wire, an electric current is induced in the copper coils as the magnetic field moves and changes. This type of device is known as a solenoid. The small current produced by the solenoid can be detected by a galvanometer. A galvanometer is simply an ammeter that detects very small currents. The galvanometer in this experiment is a compass surrounded by a copper wire coil. The small current produced by the solenoid travels to the galvanometer and the current is indicated by the deflection of the compass needle.

Experiment 4. Build a DC Motor
An electric motor converts electrical energy into mechanical energy. A generator, on the other hand, converts mechanical energy into electrical energy. Both types of energy converters use the same principle to change one form of energy into another—they use properties of magnetism. In essence, every motor can be a generator and every generator can be a motor.

For this simple DC motor, electric charge flows (electric current) through the coil armature from a direct current power source (a battery). Direct current (DC) is current that travels in only one direction. A property of a moving electric charge is that it produces a magnetic field. Therefore, a magnetic field forms around the wires in the coil armature when current flows through it. The direction of the magnetic field is perpendicular to the loop face through the middle of the loop. (Use the “right-hand rule” to determine the direction of the magnetic field produced by a current-carrying loop—curl your fingers on your right hand in the direction of the current flow in the loop. Your thumb will point in the direction of the “north end” of the magnetic field (see Figure 5). A constant external magnetic field (a magnet) is then applied. The repulsion and attraction of the magnetic fields produced by the current through the coil armature and the external magnet generate a rotational force on the coil armature that causes it to spin—electrical energy from the battery is converted into mechanical energy. The rotational force arises because the fields tend to align themselves so that they point in the same direction. The “direction” of a magnetic field is defined to point from the south pole to the north pole in a bar magnet. The tendency for magnetic fields to align explains why the north poles (or south poles) of two bar magnets repel each other. When the north poles of two magnets point at each other, the magnetic fields of these magnets point in opposite directions. If one magnet is secured to a table and the other is free to spin, the rotational force produced between the two magnets would cause the freely-spinning magnet to turn 180° so that its north pole points in the same direction as the north pole of the secured magnet. The same phenomenon occurs with the spinning current-carrying coil armature and the external bar magnet. When the magnetic fields are out of alignment, an induced rotational force tends to bring the magnetic fields into alignment and causes the coil armature to spin in the process.

In order for the motor to work, however, the coil armature must continue to spin. For this to occur, the magnetic fields must either change direction, or disappear once the magnetic fields are aligned. Once the magnetic fields are aligned they will tend to stay in line and the spinning will stop. For this simple DC motor, the magnetic field in the coil armature disappears every 180° (approximately) because the current flows through the coil armature only when the exposed copper on the axles of the armature comes in contact with the copper posts connected to the electrical power source. When the insulating enamel coating is in contact with the copper posts, the electrical circuit is open and no current flows. When there is no current there is no magnetic field in the coil armature.

The largest rotational force occurs when the magnetic fields produced by the current in the coil armature and the external magnet are at right angles to each other. The direction of the induced spin is determined by the direction the current is traveling in the coil and the external magnetic field direction. The coil will spin in the direction that will align the magnetic fields. (The motor will spin in a definite direction that can be switched by changing the direction of the current or by changing the polarity of the magnet.) The rotational force will spin the armature until the current is broken as insulated enamel contacts the copper posts. The coil continues to spin due to its momentum until the current flows 180° later and the magnetic field is produced again. The rotational force rotates the armature in the same direction as before to align the magnetic fields so the force adds to the momentum the coil already has and the coil spins faster.

Experiment Overview

Experiment 1. Properties of Magnets
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.

Experiment 2. Build an Electromagnet
Electromagnetism is all around us. It is a phenomenon that is the result of moving electric charges creating magnetic fields, and moving magnetic fields producing electric current. Learn the basics of electromagnetism by building a magnet from wire and a battery.

Experiment 3. Electromagnetic Induction
Investigate Faraday’s law by building a simple galvanometer to detect electric currents generated by a moving magnet.

Experiment 4. Build a DC Motor
Motors are the fundamental driving force of the modern world. It is a very rare occasion when you do not see or use the action of a motor during your daily life. So, how do they work? With this activity, build your own simple DC motor.

Materials

Safety Precautions

The materials in this lab are considered 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. 9-V batteries do not have enough electrical current to be harmful, but small shocks are possible. Do not complete the circuit with the battery for more than ten-second intervals. Since there is very little resistance in the wires, the battery can discharge quickly and become very hot if it is connected for a longer duration. Care should be taken when wrapping and unwrapping the wire. The pointed ends of the wire are hazardous to eyes. Wear safety glasses. Please follow all normal laboratory safety guidelines. Wash hands thoroughly before leaving the laboratory.

Procedure

Experiment 1. Properties of Magnets

Observations

1. 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 in 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 6).
    {13457_Procedure_Figure_6}
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 magnet.
17. Line the two magnets up, north pole to south pole, about 2 cm apart as shown in Figure 7. Transparent tape can be used to secure them to the table if necessary. 
    {13457_Procedure_Figure_7}
18. Place two index cards over the magnets so that the index cards overlap (see Figure 7). 
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 19–22.
24. When the experiment is complete, neatly pour the iron filings back into the weighing dish.

Magnetic Properties of Different Materials

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

Experiment 2. Build an Electromagnet

1. Obtain 75 cm of magnet wire, an iron nail, a piece of sandpaper, a compass, 9-V battery, battery clips with alligator clip leads, and 10 steel paper clips.
2. Use the sandpaper to completely sand off about 2 cm of red enamel at both ends of the magnet wire to expose the shiny copper underneath.
3. Tightly and neatly wrap the magnet wire around the nail starting at the head (flat end) of the nail. Leave about 3 cm of wire free at each end so that the alligator clips can be easily attached (see Figure 8). Make sure the wire is always twisting in the same direction. If the end of the nail is reached before all the magnet wire is wrapped, do not begin wrapping down the nail “backwards.” Instead, bend the magnet wire back down the length of the nail to the original starting position, and then wrap the wire in the same direction as before. Wrapping this way keeps the current flowing in the same direction around the nail and produces a stronger electromagnet.
   {13457_Procedure_Figure_8}
4. Place about 10 steel paper clips on the tabletop.
5. Connect the alligator clip leads to the ends of the magnet wire.
6. Connect the battery clip to the 9-V battery.
7. How many paper clips can be picked up with the electromagnet? Do not operate the electromagnet for more than 15 seconds. Disconnect the battery and record the number of paper clips in the worksheet.
8. Position the pointed end of the nail electromagnet about 3 to 4 cm from the compass.
9. Connect the electromagnet to the battery.
10. Observe the deflection of the compass needle. Which end of the compass needle points at the electromagnet? How far away can the electromagnet be from the compass and still deflect the compass needle? Disconnect the battery and record your observations in the worksheet.
11. Carefully slide the coiled magnet wire off the iron nail. It may be necessary to loosen it up slightly.
12. Repeat steps 4–10 with only the coil of wire.
13. Before leaving the lab station, carefully unwind the coil of wire so there are no kinks or loops in the wire for the next lab group.

Electromagnetic Induction

1. Obtain two 2-m lengths of magnet wire, bottle preform, 60-mL plastic jar, piece of sandpaper, neodymium magnet, two connector cords, some transparent tape and compass.
2. Use the sandpaper to completely sand off about 2 cm of red enamel at both ends of each piece of magnet wire to expose the shiny copper underneath.
3. Use a small amount of transparent tape to secure one end of one of the 2-m magnet wire pieces to the outside of the bottle preform below the neck. Leave about 3 cm of magnet wire free to be connected to the alligator clips.
4. Tightly and neatly wrap the magnet wire around the bottle preform as shown in Figure 9.
   {13457_Procedure_Figure_9}
5. Leave about 3 cm of magnet wire at the end and use a small amount of tape to secure the loose end of the magnet wire to the bottle. Make sure the free ends of the magnet wire are accessible and can be connected with the alligator clips.
6. Repeat steps 2–5 with the 60-mL plastic jar. Remove the lid to the jar and begin wrapping just below the lip of the jar so the magnet wire stays in place (see Figure 10).
   {13457_Procedure_Figure_10}
7. Connect the magnet wire wrapped around both containers together with the connector cords according to Figure 11. Make sure the connector cords are fully extended so that the two plastic containers are about 40 cm apart.
   {13457_Procedure_Figure_11}
8. Lay the 60-mL plastic jar on its side and place the compass inside the jar so that the needle moves freely.
9. Rotate the jar so that the compass needle points towards the wall of the container (perpendicular to the length of the jar) (see Figure 11). Make sure the compass lies flat so the compass needle can turn freely.
10. Once everything is connected, the compass needle is turning freely and the connector cords are fully extended, secure the connector cords to the tabletop with transparent tape. Tape the connector cords down a few centimeters from the 60-mL plastic jar so that the jar and compass will not wiggle when the connector cords move.
11. Obtain the neodymium magnet.
12. Drop the magnet into the bottle preform and observe the compass needle in the plastic jar. Does the compass needle move? Record your observations in the worksheet. Note: Keep the bottle preform about 40 cm away from the compass so the neodymium magnet’s magnetic field does not deflect the compass needle.
13. Carefully twist and tilt the bottle preform to slide the magnet up and down the tube (and into and out of the coiled magnet wire). Observe the deflection of the compass needle as the magnet moves into and out of the coils. Does the compass needle deflect more when the magnet travels faster? Is the compass needle affected more when the magnet quickly changes direction? Does the compass needle deflect when the magnet is at rest? Allow the magnet to rest inside the coils for a moment, and then quickly tip the container so the magnet slides away from the coils. Record your observations in the worksheet.
14. Obtain a stirring rod or long pencil and tape the neodymium magnet to the end.
15. Carefully move the magnet up and down inside the plastic tube using the rod. Observe the movement of the compass needle. Increase the speed of the oscillations. Is there any change in the “strength” of the deflection of the compass needle?
16. Disconnect all the wires.
17. Before leaving the lab station, carefully unwind the coil of wire so there are no kinks or loops in the wire for the next lab group.

Build a DC Motor

1. Obtain 60 cm of magnet wire and a tube or rod approximately 2 cm in diameter (e.g., pen, PVC pipe, battery).
2. Tightly wind the magnet wire around the tube or rod to create a thinly-coiled loop. Wind completely (approximately 15–20 coils) and leave 2–3 cm of free wire at both ends. The two free ends of the wire should be 180° apart when the winding is complete.
3. Carefully pull the coil off the tube or rod.
4. To secure the loop shape permanently, wrap each free end through the loop and around the coil of wire 2 to 3 times. Make sure the binding loops are 180° apart and wrapped tightly around the coil wires. Straighten the free ends so that they are perpendicular to, but in the same plane, as the coil to serve as the axle to the coil armature (see Figure 12).
   {13457_Procedure_Figure_12_Coil armature}
5. Check the balance of the coil armature by spinning the coil by the axles between your thumb and index fingers. Make sure the coil spins smoothly.
6. Obtain a small piece of sandpaper. Hold the coil at the edge of a table so the coil is straight up and down and one of the free ends is lying flat on the table. With the sandpaper, sand off the top half of the insulating enamel. Leave the bottom half of the enamel intact. Do the same to the other free end. Make sure the shiny bare copper side faces up on both ends (see Figure 12).
7. Obtain two 8-cm long pieces of 16 gauge copper wire (uninsulated).
8. Use needle-nose pliers to make a small, complete loop at one end of each piece of copper wire. If necessary, use the needle-nose pliers to straighten the copper wires as well (see Figure 13).
   {13457_Procedure_Figure_13}
9. Obtain an 8 x 8 cm foam block.
10. Insert the copper wire posts into the foam block so the loops are approximately 5 cm apart and about 3 cm above the foam surface.
11. Place the coil armature axles into the loops in the copper wire posts. The axle of the coil armature should be parallel to the foam surface and the armature should be balanced and spin freely (see Figure 13).
12. Place the ceramic magnets on the foam block directly beneath the coil armature.
13. Connect one alligator connector cord to the base of each copper wire post. Connect the other ends to a 9-V battery.
14. To start the DC motor, give the coil armature a slight spin. If it does not begin to spin continuously, give the motor a spin in the opposite direction. If it still does not spin continuously see Tips section.
15. Observe the motion of the motor and record your observations in the worksheet. What direction does it spin? How fast does it spin? Where is the magnet positioned for the best performing motor?
16. If extra time is available, produce another coil armature with fewer or more windings or a smaller or larger diameter and compare the performance of this armature to the original.

Student Worksheet PDF

13457_Student1.pdf