Download 13.3 Oersted`s Discovery

13.3 Oersted’s Discovery
In this section, students study the principle of electromagnetism and the right-hand rule for a conductor.
Achievement Chart
Categories
Assessment Opportunities/Specific
Expectation Addressed
Assessment Tools
Knowledge/Understanding
Practice questions
Understanding Concepts, q. 1–3
EM1.04, EM1.05
Section 13.3 Questions
Understanding Concepts, q. 1–3
EM1.04, EM1.05
Activity 13.3.1
Observations, a–b
EM1.04, EM1.05, EM2.02
Section 13.3 Questions
Reflecting, q. 4
EMV.03
Activity 13.3.1
Observations, c
EM1.04, EM1.05, EM2.02
Rubric 1: Knowledge/Understanding
Inquiry
Communication
Making Connections
Rubric 2: Inquiry Skills
Rubric 3: Communication
Rubric 4: Making Connections
Expectations Addressed
Overall Expectations—EMV.01, EMV.02, EMV.03
Overall Skills Expectations—SIS.01, SIS.02, SIS.06, SIS.09, SIS.10
Specific Expectations:
• EM1.04 describe and illustrate the magnetic field
• EM2.02 interpret and illustrate, on the basis of
produced by an electric current in a long straight
experimental data, the magnetic field produced by a
conductor and in a solenoid
current flowing in a long, straight conductor and in a coil
• EM1.05 analyze and predict, by applying the right-hand
rule, the direction of the magnetic field produced when
electric current flows through a long, straight conductor
and through a solenoid
BACKGROUND INFORMATION
Hans Christian Oersted was a Danish chemist and physicist
who in 1806 became a professor at the University of
Copenhagen. There his first physics research dealt with
electric currents and acoustics. During a lecture in 1820,
Oersted discovered evidence of the relationship between
electricity and magnetism. Evidently, Oersted actually made
this discovery by accident. While demonstrating electricity
he happened to have a wire above a compass. When he
turned the circuit on, the needle of the compass swung
around nearly perpendicular to the wire.
In 1824, Oersted founded a society devoted to help
spread scientific knowledge among the general public. This
society awards the Oersted Medal for outstanding
© 2002 Nelson Thomson Learning
contributions to the physical sciences. In 1932 the name
“oersted” was adopted for the unit of magnetic field strength.
One of the consequences of using the electric current
convention over electron flow is that now we must use righthand rules instead of left-hand rules. Keep in mind that
electron flow coupled with the left-hand rule for conductors
is equivalent to electric current and the right-hand rule for
conductors.
The right-hand rule and electric current are the
conventions used in university and college, so the students
will be better prepared. In the new grade 12 math course
(algebra), a right-hand rule is used for the vector cross
product, so there will be more uniformity in the approach
this way.
Unit 5 Electricity and Magnetism 345
ADDRESSING ALTERNATIVE
CONCEPTIONS
Students often do not understand the three-dimensional
nature of the magnetic field around a long, straight
conductor. They sometimes miss that the field gets weaker
as the distance from the wire increases, or they do not draw
the magnetic field lines farther apart to represent this.
Students often have trouble picturing the true nature of
the field around a long, straight wire so careful observations
during any activities and close attention to the diagrams in
the text (especially Figure 2) can help with this.
• Groups for the activity should be small, if possible. If you
are short on equipment, part of the activity could be
demonstrated.
• A fairly large current is required to produce a noticeable
magnetic field pattern around a single conductor such as
this. Fortunately, the current needs to be on for only a
second or two. Emphasize this with the students to avoid
drained batteries or overloaded power supplies, since the
resistance of the circuit is so low as to be almost a short.
• For maximum deflection, the compasses should be placed
as close to the wire as possible.
Related Background Resources
Nelson Web site:
www.science.nelson.com
for specific Web links
PLANNING
Suggested Time
Narrative/Practice—10 to 15 minutes
Activity 13.3.1—20 to 25 minutes
Section Questions—5 to 10 minutes
Core Instructional Resources
• Solutions Manual
• Colour Transparencies
• Lab and Study Blackline Masters
TEACHING SUGGESTIONS
• You could initially demonstrate electromagnetism and
then allow the students to discover the principles behind
electromagnetism in Activity 13.3.1. A comparison could
be made between electron flow and the left-hand rule,
showing that they are equivalent ways of predicting the
direction of the magnetic field.
Activity 13.3.1
• Treat this activity as a discovery lab–based activity with
very little preparation. Allow students to get the basic
ideas from first-hand experience, and then pull it all
together in a more structured format.
• When discussing the results of the activity, have a wire set
up on an overhead with transparent compasses available
for quick testing of the principles and rules.
346
Chapter 13 Electromagnetism
ACTIVITY 13.3.1
Magnetic Field of a Straight Conductor
• Students will investigate the characteristics of the
magnetic field around a straight conductor.
BEFORE
Teacher Preparation
Time: 20 to 25 minutes
Materials and Equipment:
Each group of two or three students will need
20 cm of bare 12-gauge copper wire
piece of stiff cardboard, 15 cm × 15 cm
battery (6 V–12 V) or DC power supply
iron filings
connecting wires with alligator clips
four compasses
Safety and Disposal:
• Students should keep their hands away from their face and
eyes during the activity and wash their hands afterward.
• They should also clean the workstation of iron filings.
• Students should touch the wire to terminals for only short
periods of time. The wire can get very hot very fast.
Assessment:
• Discuss students’ observations after the activity.
• Have them hand in a report.
• Blackline Master for extra practice drawing fields around
conductors.
Student Preparation
• This can be treated as a discovery activity with little or no
pre-lab discussion.
© 2002 Nelson Thomson Learning
DURING
• Be safety conscious at all times.
• Help students spot patterns in the iron filings only if
necessary.
AFTER
• Discuss the characteristics of the magnetic field.
• Formulate the right-hand rule for conductors.
• Ask students to predict and draw the field around the
conductor demo on the overhead projector.
(Sample answers follow.)
• (a) The magnetic field around a straight conductor is
circular around the axis of the conductor. Compass needles
indicate that the direction of the magnetic field is that
predicted by the “right-hand rule” for straight conductors.
© 2002 Nelson Thomson Learning
• (b) The magnetic field lines are not as pronounced farther
from the conductor, indicating that the strength of the
magnetic field is weaker at greater distances from the
conductor.
• (c) The right-hand rule for straight conductors provides an
adequate description of the shape and orientation of the
magnetic field around a straight conductor. It properly
predicts that when the thumb of the right hand points in
the direction of the electric current through the straight
conductor, the curled fingers of the right hand point in the
direction of the magnetic field surrounding the conductor.
Extensions/Modifications:
• Try different electric potential differences and determine
the effect on the magnetic field.
Unit 5 Electricity and Magnetism 347