Materials Included In Kit

Additional Materials Required

Prelab Preparation

1. Measure and cut approximately 4.5 meters of magnet wire for each group. Or, cut the magnet wire into 1.8-m lengths and 75-cm lengths. Each group needs two 1.8-m lengths and one 75-cm length.
2. Cut the sandpaper sheet into 1" x 4" pieces. Each group needs one 1" x 4" piece.

Safety Precautions

While 9-volt batteries are not harmful, a small shock is 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.

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 should be saved for future use. All the materials may be disposed of according to Flinn Suggested Disposal Method #26a.

Teacher Tips

• Enough materials are provided in this kit for eight groups of students. 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 or 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.
• The wire can also be left wrapped around the tubes and nails to save time with future classes.

Sample Data

Observations

Magnetism produced by a current-carrying wire

Initial direction of the red tip of the compass needle.

The red end of the compass needle pointed toward the North Pole of the Earth.

Effect of the magnet on the compass needle.

The magnet made the compass needle spin around, and eventually the needle pointed at the magnet. The compass needle end that pointed at the magnet was dependent on the pole of the magnet that faced the compass. The red end pointed to the south pole of the magnet. The white end pointed to the north pole of the magnet.

Direction of the red tip of the compass needle with electric current traveling through the wire. What happens when the current is reversed?

The red tip of the compass needle was deflected counter-clockwise around the vertical wire. The needle always appeared perpendicular to the wire, no matter where it was positioned around the wire. The needle did not point at the current-carrying wire. When the current was reversed, the red tip of the compass needle was deflected clockwise around the vertical wire.

Effect on the compass needle by the horizontal current-carrying wire. What happens when the current is reversed?

When the compass needle was lined up parallel to the uncharged wire, and the current was switched on, the compass needle was deflected so that it rotated and remained perpendicular to the wire. When the battery was disconnected, the compass needle returned to its original (“natural”) direction. When the current was reversed, the compass needle again deflected perpendicular to the current-carrying wire, but the red tip of the compass needle pointed in the opposite direction.

Building an electromagnet

Number of paper clips picked up by the electromagnet (with iron 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 iron 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.

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.

Answers to Questions

1. Since the compass needle is deflected by a magnetic field (the neodymium magnet), what does it mean when an electric current deflects a compass needle?

   The compass needle is deflected by the magnetic field of the magnet. Therefore, the current traveling through the wire must be producing a magnetic field because the compass needle is deflected only when the battery is connected to the wire.

2. When the electric current is traveling through the vertical wire, does the compass needle ever point towards the wire?

   No, the compass needle always points perpendicular (tangent) to the wire and follows either a clockwise or counter-clockwise direction around the wire, depending on the direction of the current through the wire.

3. Based on your observations, what is the general shape of the magnetic field surrounding a current-carrying wire?

   Based on the observations of the magnetic field produced by a current-carrying wire, the magnetic field has a circular shape around the wire. The “direction” of the magnetic field depends on the direction of the current (according to the Right-Hand Rule).

4. What direction does the compass needle deflect when a horizontal current passes over the compass? What direction does the needle point when the current is reversed?

   When the compass needle is parallel to the wire initially, the compass needle deflects 90 degrees, so that it becomes perpendicular to the wire, when current travels through it. When the current direction is reversed, the compass needle again rotates 90 degrees to become perpendicular to the wire, but the red tip of the compass needle points in the opposite direction.

5. 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.

6. 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).

7. 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.)

Introduction

Electromagnetism is all around us. Electromagnetism generates motion (electric motors), allows us to see our world (visible light), and provides the means for communicating long distances (microwaves used by cell phones). Learn the basics of electromagnetism by studying the magnetic properties of electric current-carrying wires. Then, coil a current-carrying wire around a nail to make an electromagnet. Finally, investigate Faraday’s law by building a simple galvanometer to detect electric currents generated by a moving magnet.

Concepts

• Magnetic properties of current-carrying wires
• Electromagnetic induction
• Electromagnets
• Faraday’s law

Background

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 1). 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 material, 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 produce a very strong magnet—an electromagnet.

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.

Materials

Safety Precautions

While 9-volt batteries are not harmful, 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 normal laboratory safety guidelines.

Procedure

Part I. Magnetism produced by a current-carrying wire

1. Obtain a foam cup, compass, two connector cords with alligator clips, index card, 6-volt or 9-volt battery, neodymium magnet, 25 cm of magnet wire, piece of sandpaper, pair of scissors and some transparent tape.
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. Use scissors to cut a 3" x 3" opening in the side of the foam cup as shown in Figure 2.
   {12024_Procedure_Figure_2}
4. Carefully poke a tiny hole through the center of the bottom of the foam cup with the magnet wire.
5. Place the foam cup upside down on the tabletop and slide the magnet wire through the hole so that it is vertical.
6. Bend the magnet wire at the base of the cup as shown in Figure 2 so that the wire is supported by the tabletop and extends out of the side opening in the cup. Leave approximately 9 cm of magnet wire extending vertically above the inverted cup.
7. Use a small amount of transparent tape to secure the wire to the tabletop (see Figure 2).
8. Adjust the position of the foam cup so that the magnet wire is vertical. Then, use a small amount of transparent tape to secure the cup to the tabletop.
9. Use the pointed end of a pair of scissors or a sharp pencil point to poke a hole through the center of the index card.
10. Slide the index card over the magnet wire and allow it to rest on the bottom of the cup (see Figure 2).
11. Clip the connector cords to the exposed copper ends of the magnet wire. It may be necessary to bend the end of the magnet wire taped to the tabletop upwards in order to clip it with the alligator clip as shown in Figure 3. Make sure the magnet wire that extends vertically above the cup does not bend and remains vertical and rigid. Also, make sure the connector cord does not interfere with the index card. The index card should remain flat and horizontal. Note: Do not connect the connector cords to the battery until it is time to do the experiment.
    {12024_Procedure_Figure_3}
12. Place the compass on the index card adjacent to the vertical wire (see Figure 3). 
13. Observe the orientation of the compass needle. Record the initial direction of the red tip of the needle on the worksheet.
14. Bring the neodymium magnet near the compass. Observe the effect on the compass needle by the magnetic field of the magnet. Remove the magnet from the experiment setup. Record your observations on the worksheet.
15. Connect the free ends of the connector cords to the battery.
16. Observe the direction the compass needle points after connecting the battery. Quickly move the compass around the wire and observe the direction of the needle. Does the red tip of the needle point clockwise or counter-clockwise as the compass is moved? Disconnect the battery and then record the direction of the red tip of the compass needle on the worksheet. Caution: Do not allow the battery to be connected for intervals more than 10 seconds.
17. Repeat steps 15 and 16 but reverse the connecting leads on the battery so that the current travels in the opposite direction.
18. Disconnect the alligator clips from the magnet wire and carefully remove the tape from the foam cup and tabletop (save the cup for future use). Remove the magnet wire from the cup and straighten it.
19. Lay the compass on the tabletop. Then place the straight magnet wire over the compass so that the wire and compass needle are parallel to each other.
20. Connect the connector cords to the ends of the magnet wire.
21. Connect the free ends of the connector cords to the battery and observe the compass needle. Which direction does the red tip of the compass needle point? Record your observations on the worksheet.
22. Repeat steps 20 and 21, but reverse the leads connected to the battery so the current travels in the opposite direction.
23. Disconnect the battery.

Part II. Building an Electromagnet

24. Obtain 50 cm of magnet wire, an iron nail, piece of sandpaper, compass, connector cords, 9-V battery, and about 10 steel paper clips.
25. 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.
26. 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 4). 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.
    {12024_Procedure_Figure_4}
27. Place about 10 steel paper clips on the tabletop.
28. Connect the connector cords to the ends of the magnet wire.
29. Connect the free ends of the connector cords to the 9-volt battery.
30. How many paper clips can be picked up with the electromagnet? Disconnect the battery and record the number of paper clips on the worksheet.
31. Position the pointed end of the nail electromagnet about 3 to 4 cm from the compass.
32. Connect the electromagnet to the battery.
33. 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 on the worksheet.
34. Carefully slide the coiled magnet wire off the iron nail. It may be necessary to loosen it up slightly.
35. Repeat steps 27–33 with only the coil of wire.

Part III. Electromagnetic Induction

36. Obtain two 1.8-m lengths of magnet wire, bottle preform, 60-mL plastic jar, piece of sandpaper, neodymium magnet, two connector cords, some transparent tape, and compass.
37. 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.
38. Use a small amount of transparent tape to secure one end of one of the 1.8-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.
39. Tightly and neatly wrap the magnet wire around the bottle preform as shown in Figure 5.
    {12024_Procedure_Figure_5}
40. 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.
41. Repeat steps 38–40 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 6).
    {12024_Procedure_Figure_6}
42. Connect the magnet wire wrapped around both containers together with the connector cords according to Figure 7. Make sure the connector cords are fully extended so that the two plastic containers are about 40 cm apart.
    {12024_Procedure_Figure_7}
43. Lay the 60-mL plastic jar on its side and place the compass inside the jar so that the needle moves freely.
44. Rotate the jar so that the compass needle points towards the wall of the container (perpendicular to the length of the tube) (see Figure 7). Make sure the compass lies flat so the compass needle can turn freely.
45. 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.
46. Obtain the neodymium magnet.
47. Drop the magnet into the bottle preform and observe the compass needle in the plastic jar. Does the compass needle move? Record your observations on 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.
48. 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 on the worksheet.
49. Obtain a stirring rod or long pencil and tape the neodymium magnet to the end.
50. 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 magnitude of the deflection of the compass needle?
51. Disconnect all the wires. Save the magnet wire according your teacher’s directions.

Student Worksheet PDF

12024_Student1.pdf