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Subject: College Prep/Conceptual Physics
Grade Level: High School—9th – 12th grades
Lesson: Electromagnets: Winding Things Up!
Type of Lesson: Inquiry Lab Activity
Teacher: Michelle Boggs
Length of Lesson: 45 min.
Rationale: This activity is a good way for students to discover how solenoids and
electromagnets work without having (much) prior knowledge about either. In order
for students to be successful in this activity as it is written, they will need to have a
basic understanding of both electricity and magnetism. This lesson can be used to
introduce electromagnetic force, and help students better understand what
electromagnets are and how solenoids work.
Math Skills needed: For this particular lesson, students will be creating and
interpreting graphs of the data that they collect, so they will need to be familiar with
creating line graphs. In addition, however, students in a class where this lesson would
be taught would at least need to have had basic Algebra I skills in order to get them
through the material leading up to this activity (e.g. ohm’s law, coulomb’s law, etc.).
Prior Graphing Calculator/CBL skills: To successfully complete this entire lesson in a
50-minute allotted class period, students should be proficient in the use of the Texas
Instruments graphing calculator and CBL-2 data collection interface. DataMate is a
program that comes with a CBL-2 and can easily be downloaded onto the graphing
calculators. However, if your students are not familiar with the equipment or the
DataMate program, this lesson can be adapted to skip the measurement of magnetic
field while just creating an electromagnet and measuring strength by the number of
paper clips that can be picked up with the nail with different numbers of coils of wire
wrapped around the nail.
Ohio Standards, Benchmarks and Indicators:
Physical Science: (Grades 9-12)
Nature of Energy:
1. Trace the transformations of energy within a system (e.g., chemical to electrical to
mechanical) and recognize that energy is conserved. Show that these transformations
involve the release of some thermal energy.
Forces and Motion:
2. Explain how electric motors and generators work (e.g., relate that electricity and
magnetism are two aspects of a single electromagnetic force). Investigate that electric
charges in motion produce magnetic fields and a changing magnetic field creates an
electric field.
Materials:
6V battery (could also use size D)
Alligator clips (or tape)
Large iron nails
Texas Instruments® CBL2TM
Small paper clips--at least 20 per group
DataMate Program
Vernier Magnetic Field Sensor
Insulated wire
TI-83 Plus® graphing calculator
Objectives:
1.
2.
Students will create an electromagnet using insulated wire, an iron nail, and a
battery, and they will measure the strength of the magnetic field of their
electromagnets.
Students will determine that the strength of the magnetic field of an
electromagnet is directly related to the number of coils of wire wrapped
around their nail.
Introduction and Background Material:
This material can be given to students in the form of notes that they should right
down, or it can be summarized into reading material and typed into the lab handout.
If a discovery/inquiry approach is desired, the information in the notes can be
discussed after the activity, so that students really are discovering how
electromagnets work without prior knowledge.
Students should understand that electricity and magnetism are different
aspects of a single force known as the electromagnetic force. The electric force
results from charged particles, and the magnetic force usually results from the
movement of electrons in an atom. Both aspects of the electromagnetic force are
caused by electric charges.
In addition, students should realize that magnetic fields are produced at right
angles to an electric current, and electric currents are deflected perpendicular to a
magnetic field. Changing the current in an electromagnet controls the strength and
direction of its magnetic field. Finally, electromagnetic devices change electrical
energy into mechanical energy.
Resources:
Prentice Hall, 2004. Physical Science: Concepts in Action
Physical Science with Calculators, 2000. Vernier Software & Technology.
Electromagnets: Winding
Things Up!!
A magnetic field forms around a wire that has an electric current in it, and by winding a wire
around a piece of iron, you can create a magnet. A temporary magnet made in this way is called
an electromagnet. In this experiment, you will use a Magnetic Field Sensor to study the
relationship between number of wire winds and magnetic field strength of an electromagnet.
OBJECTIVES
In this activity, you will:
· build an electromagnet
· use a TI Graphing Calculator, a CBL 2 interface, and a Magnetic Field Sensor to measure
magnetic field strength
· make a graph of the data
· make conclusions about the relationship between number of wire winds and magnetic
field strength
MATERIALS
CBL 2 interface
TI Graphing Calculator
Insulated wire- approx. 1-m long
battery (6V)
DataMate program
large iron nail
Vernier Magnetic Field Sensor
Alligator clips (or tape)
Small paper clips
Balance (centigrams)
Figure 1
PROCEDURE
1. Tape a Magnetic Field Sensor to the table top. The white side of the sensor (or white dot)
should face up and be parallel to the table top.
2. Connect the Vernier Magnetic Field Sensor to Channel 1 of the CBL 2 interface. Set the
switch on the sensor to Low. Use the link cable to connect the interface to the TI
Graphing Calculator. Firmly press in the cable ends.
3. Turn on the calculator, and start the DATAMATE program.
4. Set up the calculator and interface for the Magnetic Field Sensor.
a. Select SETUP from the main screen.
b. If CH 1 displays a Magnetic Field Sensor, proceed directly to Step 5. If it does not,
continue with this step to set up your sensor manually.
c. Press ENTER to select CH1.
d. Choose MAGNETIC FIELD from the SELECT SENSOR list.
e. Choose LO MAGNET FLD(MT) from the MAGNETIC FIELD list. The sensor will read in
units of millitesla (mT).
5. Set up the calculator and the interface for the appropriate data collection mode.
a. Press the
once to select MODE, and press ENTER .
b. Select EVENTS WITH ENTRY from the SELECT MODE menu to collect magnetic field
data as a function of distance. In this mode you will trigger the interface to record the
field for each position you choose.
c. Select OK to return to the main screen.
6. Collect the data for zero winds.
a. Select START to prepare for data collection.
b. Get a large iron nail and place its pointed end perpendicular to the top of the Magnetic
Field Sensor at its very end, as shown in Figure 1. When the reading has stabilized,
press ENTER .
c. Enter “0” (for 0 Winds), to store this magnetic field strength-winds data pair.
7. Use the alligator clips to attach one end of the insulated wire to the 6V battery. (If
alligator clips are not available, tape the wire to the bottom of a 1.5 volt flashlight battery
instead)
8. Place the nail on the wire at a position 10-15 cm from the battery. Tightly wind the wire
around the nail 3 times as shown in Figure 1.
9. Collect data for 3 winds.
a. Connect the other end of the insulated wire to the battery with another alligator clip
(or tape, if necessary).
b. A partner should again touch the pointed end of the nail to the top of the sensor at its
very end as shown in Figure 1. Important: If the reading decreases, reverse the
connections.
c. When the reading has stabilized, press ENTER . Caution: The battery will become warm
as it is used. To keep it from getting hot, and to save energy, remove one of the
alligator clips from the top of the battery immediately after ENTER has been pressed.
Enter “3” (for 3 Winds).
10. Repeat Step 9 for 6, 9, 12, 15, 18, and 21 winds. Important: Wrap all winds at nearly the
same distance from the nail end.
11. Record the magnetic field strength values (in mT).
a. Stop data collection by pressing the STO button. A graph of the magnetic field vs.
number of winds data will be displayed.
b. Use
to examine the data. As you move the cursor right or left, the number of
winds (X) and the magnetic field strength (Y) values of each data point are displayed at
the bottom of the graph.
c. Record the magnetic field strength (Y) values in your Data Table.
DATA
Winds Magnetic Field
(#)
(mT)
0
_______
5
_______
10
_______
15
_______
Winds Magnetic Field
(#)
(mT)
20
_______
25
_______
30
_______
35
_______
PROCESSING THE DATA
1. Using your above data, create a graph in Figure 2 representing the strength of
magnetic field as a function of the number of winds in your electromagnet. What
is the relationship between number of winds and magnetic field strength?
2. According to your data and graph, what would the magnetic field strength reading
be for 13 winds? For 50 winds? Explain.
3. Determine the mass of paper clips your electromagnet will pick up with the same
numbers of winds used in the above experiment. Make a comparison of mass picked
up to magnetic field strength. How many winds do you need in your electromagnet
to pick up another iron nail?
4. Compare the magnetic field of the nail after the experiment with its magnetic
field before it has been used in an electromagnet. Measure the magnetic field of
the nail again after striking it on a hard surface. Explain these results using the
idea of magnetic domains.
Figure 2.