Lab

Summary

In this lab, students will better understand that opposite charges attract each other, and like charges repel. The statement that two and only two similarly charged particles, like electrons, can inhabit the same region of space seems to contradict those observations. Students rarely have clarity about the size of the electrostatic forces of attraction and repulsion, especially their relationship to charge separation distance.

Grade Level

High school

Objectives

By the end of this lesson, students will

• qualitatively (and, if possible, quantitatively) study the forces generated by moving electrons.
• quantitatively determine the relationship between electrostatic forces and separation distance through the study of magnetic repulsion.

Chemistry Topics

This lesson supports students’ understanding of

• Electrostatic forces
• Subatomic particles

Time

Teacher Preparation: 2 hours including construction 

Lesson: 40 minutes

Materials

For each group:

• DC power source (6 V) or 6-V battery
• Copper or aluminum wire, insulated (at least 30”)
• Cardboard tube, 2-5” diameter, section
• Alligator clamps
• Ring stand and test tube clamp (preferably aluminum)
• Vernier Magnetic Field Sensor and interface/recorder
• Vernier Dual-Range Force Sensor and interface/recorder
• Two meter sticks
• Adhesive tape
• Two neodymium magnet-slide assemblies (see teacher notes for details)

Safety

No specific safety precautions are needed for this experiment.

Teacher Notes

• I put together the magnet-slide assemblies ahead of time, using pre-drilled neodymium magnets attached to a 1 x 6" piece of wood.
•  In part I, the idea is to reverse the polarity on the magnetic field, and the easiest way with a fixed magnet is to move from head-on the current loop to tail-on the current loop. In one orientation there is attraction, and the other is repulsion.  The motion is not large, but it should be clear if the students are fairly close to the action.
• See Sample Data file for expected results.

Downloads

• Teacher Guide.doc
  
• Teacher Guide.pdf
  
• Student Activity.doc
  
• Student Activity.pdf
• Sample Data.pdf
  

Submitted by:
W. Patrick Cunningham
CT Johnson High School
San Antonio, Texas

Thanks to:
PASCO

For the Student

Lesson

Purpose

• To qualitatively (and, if possible, quantitatively) study the forces generated by moving electrons.
• To quantitatively determine the relationship between electrostatic forces and separation distance through the study of magnetic repulsion.

Materials

• DC 6-V power source or 6-V battery
• Copper or aluminum wire, insulated, at least 30”
• Cardboard tube, 2–5” diameter
• Ring stand and test tube clamp (preferably aluminum)
• Two neodymium magnet-slide assemblies
• Alligator clamps
• Vernier Magnetic Field Sensor and interface/recorder (optional)
• Vernier Dual-Range Force Sensor and interface/recorder
• Two meter sticks
• Adhesive tape

 Procedure

PART I

1. Using a cardboard tube as a base, wrap several turns of insulated wire and connect one end of the wire to the DC power source at the negative pole. Clamp the tube horizontally to a ring stand. (Optional: secure the Magnetic Field Sensor so that it is inside the wire/tube assembly without touching either. Set the recorder to record the intensity of the magnetic field against time.)
2. Connect the other end of the wire carefully to the positive pole of the DC power source and turn it on.
3. Move the neodymium magnet toward the tube/wire assembly and record your visual observations (and numeric data, if applicable).
4. Move the magnet to the other side of the coil and repeat the movement and observations.
5. Disconnect the power source.

PART II

1. On a smooth table, set the two neodymium magnets facing each other and about six inches apart.
2. Lay the two meter sticks parallel to each other and next to them so that the magnets can freely move along the “track” the meter sticks make. Tape the meter sticks down.
3. Tape the Dual- Range Force Sensor so that its probe touches the nonmagnetic end of one of the magnet-slide assemblies (call it #1). See Figure 1.

Figure 1: Sensor with movable magnet-slide assemblies and two meter sticks

1. Prepare the sensor and recorder to record force (using the 0-10 N setting) vs. distance, which will be entered manually. Make certain that neither magnet-slide assembly is sticking.
2. Start with a separation distance of about 3 cm between assembly #1 and assembly #2.  Gradually move assembly #2 toward the other one, about 0.2 cm closer each time. Record the force and distance values.
3. Once the separation distance is so small that magnet-slide assembly #1 appears to be rising from the table, stop recording. Repeat at least once

Analysis

PART I

1.   What happened to the coil as you moved the magnet-slide assembly toward it?

2.   What happened when you moved the magnet-slide assembly toward it from the other direction?

3.   What was the coil-with-electrons-flowing acting like?

4.   Can you say that the circulating electrons were setting up a magnetic field with both north and south poles?

5.   Could two circulating electron loops like that attract or repel each other?

 PART II

1.   Graph distance vs. force for the magnetic repulsion data. Which is the independent variable?

2.   Using Logger-Pro analytical software or its equivalent, find the curve of best fit that appears to relate distance and force.

3.   Write the equation that relates distance and force for repelling magnets.

Conclusion

1.   From your experience in this lab, could you conclude that the same kind of mathematical relationship might hold for two oppositely charged particles, if you measured electrostatic force instead of magnetic force?

2.   From your text or notes, write the mathematical equation relating force to separation distance in Coulomb's Law. Does your lab experience confirm that relationship?

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