Electromagnets
Author:
Date Created:
Subject:
Level:
Standards:
Jane Earle, Lauren Downing, Kevin Dilley
July 2007
Physics
High School
New York State- Physics (www.emsc.nysed.gov/ciai/)
Standard 1- Analysis, Inquiry and Design
Standard 4- Moving electric charges produce magnetic
fields.
Standard 7- Interdisciplinary Problem Solving
Schedule: Two Class Periods
Objectives:
Vocabulary:
Students will understand what an
electromagnet is and how it works.
They will be able to explain the
relationship between electricity and
magnetism.
Magnet
Electricity
Electromagnet
Charge
Current
Magnetic Field
Students will:
Materials:
•
•
•
•
Experimentally discover how to
strengthen electromagnets
Establish a definition for
magnetism that incorporates its
relationship to electricity
Present/share results
Design and conduct their own
experiements
For Group:
Wire
Batteries
Bolts
Dowels
Straws
Standard Compass
Paperclips
Electrical Tape
Round Magnet
Bar Magnet
Battery Holder(s)
For Class:
Electromagnetic Lift
Object to lift†
For Each Student:
Activity Sheet 1
Station Sheets 1 - 3
†
Provided by Teacher
Safety:
Do not hold wires to battery terminals with
fingers, they get hot.
Science Content for the Teacher:
Bar Magnet
A magnet always has two poles, the North Pole and the
South Pole. By convention, magnetic field lines point
outward at the North Pole and inward at the South Pole and
form closed loops that circle the entire magnetic.
Because opposite poles (NorthSouth) attract while similar poles
(North-North or South-South) repel, the magnetic field
lines of a bar magnet can be visualized using another
magnet. A compass is an excellent tool for this. The
needle of a compass is itself a small permanent magnet
and the North indicator (typically colored red or white) is a
magnetic North Pole. The needle is free to rotate and will
tend to align itself such that the North indicator points
toward a magnetic South Pole. For example, in response
to the Earth’s magnetic field, the compass will point toward
the geographic North Pole of the Earth because it is in fact
a magnetic South Pole.
Electromagnets Lab
-2–
Electric and Magnetic Sources
The electric field of a positive point
charge is radially outward.
Electric sources are inherently
“monopole” or point charge sources.
The magnetic field of a bar magnet:
Magnetic sources are inherently dipole
sources—you can’t isolate North or
South “monopoles.”
The magnetic field produced by electric current in a solenoid coil is similar to that
of a bar magnet:
An iron core has the effect of multiplying greatly the magnetic field of a solenoid
compared to the air core solenoid on the left.
Electromagnets Lab
-3–
Electromagnet
Electromagnets are usually in the form of iron core
solenoids. The ferromagnetic property of the iron core
causes the internal magnetic domains of the iron to line
up with the smaller driving magnetic field produced by the
current in the solenoid. The effect is the multiplication of
the magnetic field by factors of tens to even thousands.
The magnetic field (B) at the center of the solenoid is:
B = µ n I , where µ = k µ0
Where n is the number of coils in the wire, I is the current
in the wire, µ0 is the magnetic permeability constant (4π x
10-7 N/A2), k is the relative permeability of the core (for iron ~200).
The magnifying effect is proportional to k, so for a solenoid with an iron core you
would expect a magnification of about 200 compared to a solenoid with an air
core.
Electromagnets Lab
-4–
Preparation:
•
•
Assemble electromagnet set-ups (battery in holder, wires from holder
attached to wire coiled around a bolt)
Organize and lay out materials
Classroom Procedure:
Engage (Time: 10mins)
Divide students into groups of 2 or 3. Hand out one battery, one holder,
one wire coiled around a bolt and one compass to each group (This set up can
be pre-assembled). Each group must move their compass around the set up to
test for magnetism.
During this time, the facilitator should circulate between groups
challenging those who have been able to make the compass move to see if they
can get it to point in another direction. All observations should be recorded.
After about 10 minutes, groups should be asked to share their results. Any
hypotheses about the relationship between electricity and magnetism should be
recorded.
Ask students what questions they have about the electromagnet set up
and how it works. Divide students into small groups based on the questions they
are interested in “researching.” Groups will design their own experiments in an
attempt to begin to answer the questions they have posed. A variety of materials
will be made available to each group. In order to pick up these materials, groups
must establish an initial plan for their experiment, and have it approved by the
facilitator, so that they do not overwhelm themselves with unnecessary materials.
Materials can always be changed or added later in the experiment.
Explore (Time: 30mins)
During this time student groups will research various aspects of the
phenomenon they have just observed. Possible examples include: Why are the
coils important, What if we use more batteries or a different kind of battery, What
is the best material to use in the core, is our hypothesis about the relationship
between electricity and magnetism true apart from the “electromagnet,” how do
the filed lines in the electromagnet set up differ from a bar magnet?
Each group will design and conduct their own experiment. Data should be
collected and organized in some form so that it can be later shared with the
larger group. Groups interested in testing the strength of their electromagnet(s)
should use the ability to pick up paper clips as their measure. Students should be
reminded that they can measure in any way they’d like, but they need to be
precise and consistent.
Electromagnets Lab
-5–
The facilitator should aid in the provision of materials as well as pose new
questions to idle groups.
Explain (Time: 20mins)
Each group should share their experiment design and its results with the
larger group. Students should be encouraged to ask questions about their
classmates’ experiments.
The facilitator should then bring out the electromagnetic lift and
demonstrate how it works using a chair or other heavy object. Each group should
then attempt to explain how the lift works and why it is so strong from the
perspective of the research they did.
Electromagnets Lab
-6–
Assessment:
The following rubric can be used to assess students during each part of
the activity. The term “expectations” here refers to the content, process and
attitudinal goals for this activity. Evidence for understanding may be in the form of
oral as well as written communication, both with the teacher as well as observed
communication with other students. Specifics are listed in the table below.
1= exceeds expectations
2= meets expectations consistently
3= meets expectations occasionally
4= not meeting expectations
Engage
Explore
Explain
1
Shows leadership in the
discussion and offers
creative ideas reflecting a
good understanding of
magnetism and electricity.
Provides an in-depth
explanation of findings,
makes excellent use of
vocabulary and examples.
2
Participates in the
discussion and shows an
understanding of electricity
and magnetism.
Contributes to the
discussion, but shows little
understanding of electricity
or magnetism.
Does not participate in
discussion. Shows no
understanding of electricity
or magnetism.
Designs and conducts
experiment creatively and
scientifically while providing an
explanation for what is
observed. Works very well with
group.
Designs and conducts
experiment creatively and
scientifically. Works
cooperatively with group.
Works cooperatively with group,
but makes some mistakes with
the procedure.
3
4
Has trouble working with group.
Does little to complete the
procedure.
Electromagnets Lab
-7–
Provides clear explanation
of findings. Makes good
use of vocabulary, provides
some examples.
Provides a limited
explanation of findings.
Uses a few vocabulary
words or examples.
Is not clear in explanation
of findings. Does not make
use of vocabulary or
examples.
Extension Activity:
With the knowledge you’ve gained from this activity, build an electromagnetic
motor! Instructions are in the “activity sheets” part of this module.
Safety:
Do not hold wires to battery terminals with fingers, they get hot.
Acknowledgments:
http://www.physics.sjsu.edu/becker/physics51/images/28_03_Earth_magnetic_field.jpg
http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/elemag.html
Electromagnets Lab
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