Teaching the
Concept of
Magnetic Fields
Daniele Cerone
Jincy Binoy
Introduction to Magnetic Fields
Yes
It has a
magnetic
field
To be continued
Introduction to Magnetic Fields
•
A magnetic field is defined as a change in energy within a volume of
space that is produced by electric charges in motion.
•
Electrons, a point charge, also produce magnetic fields that are dependent on the
acceleration, velocity, and charge of the individual particles.
•
The presence of a magnetic field at a point surrounding a magnet is
represented by a vector field with a magnitude (specifying its strength)
and a direction.
•
The strength of a magnetic field is highest at the poles and the field lines
are always in the direction from North to South Pole.
•
A Lorentz Force is exerted on an electrically charged particle in motion within a magnetic
field at any given point. The magnitude of the Lorentz force is dependent the electric
charge, q, and the velocity of the particle, v, within the magnetic field.
•
Some properties of magnetic lines of force include that: each have the same strength, an
increase in distance from the poles of a magnet result in a lower density, they seek the
path of least resistance, and they never intersect.
Lesson Sequence

Lesson 1: Introduction to Magnetic Fields
 Magnetic Force Fields
 Domain Theory of Magnetism

Lesson 2: Magnetic Fields II
 Magnetic Field of a Straight Conductor, Current Loop, and Solenoid

Lesson 3: Magnetic Forces on Moving Charges
 Measuring Magnetic Fields
 Right Hand Rule for the Direction of Magnetic Force, Charge-to-Mass Ratios

Lesson 3: Magnetic Force on a Current Carrying Conductor
 Right Hand Rule For The Motor Principle

Lesson 4: Ampere’s Law
 The Ampere as a Unit of Electrical Current
 Application: Coaxial Cables

Lesson 5: Electromagnetic Induction

Application: Coaxial Cables
Curriculum Expectations
•
D1.2 assess the impact of an electromagnetic technology that is used for
the benefit of society or the environment [AI, C]
•
D2.1 use appropriate terminology related to electricity and magnetism, including, but not limited to:
permanent magnet, electromagnet, magnetic field.[C]
•
D2.4 conduct an inquiry to determine the magnetic fields produced by a permanent magnet, a
straight current-carrying conductor, and a solenoid, and illustrate their findings [PR, AI, C]
•
D2.5 conduct an inquiry to determine the direction of the magnetic field of a straight currentcarrying conductor or solenoid [PR, AI]
•
D2.6 conduct an inquiry to determine the direction of the forces on a straight current-carrying
conductor that is placed in a uniform magnetic field [PR, AI]
•
D3.4 describe, with the aid of an illustration, the magnetic field produced by permanent magnets
(bar and U-shaped) and electromagnets (straight conductor and solenoid)
•
D3.7 state Oersted’s principle, and apply the right-hand rule to explain the direction of the magnetic
field produced when electric current flows through a long, straight conductor and through a solenoid
Teaching Approach
Magnetic Field
A video demonstration
http://www.youtube.com/watch?
v=zbTrHWW3xvU
Teaching Approach
Inquiry based approach to teach
tracing Magnetic field : Physical lab
Students can find out the magnetic field lines using compass and bar magnet.
They will explore , what happen to magnetic field lines, when two magnets
place N pole pointing N and S pole pointing north…..
Students can manipulate various features within the laboratory, which will
assist them in their investigation and follow up questions
Teachers can use the follow up questions as an assessment tool for student
understanding
Teaching Approach
Inquiry based approach to teach
Magnetic Forces on Moving Charges & conductors:
Virtual lab
(Gismos lesson plan)
http://www.explorelearning.com/
index.cfm?method=cResource.dsp
View&ResourceID=611
Teaching Approach
Ampere’s Law
Power point presentation
Recall that the magnetic field around a straight
conductor consists of field lines that are concentric
circles, centred on the conductor. The circles
become more widely spaced as the distance from
the conductor increases.
M(I/2
So, strength of magnetic field,
B α 1/r ,
Were r is the radius of the circle
Also we know that, the
strength of the magnetic
field B, increases as the
current, I ,through the
conductor increases,
B αI
B α I/r
B=kI/r,
Were K is where k is a
proportionality constant
Ampère’s Law
Along any closed path through a magnetic
field, the sum of the products of the
scalar component of B , parallel to the
path segment with the length of the
segment, is directly proportional to the
net electric current passing through the
area enclosed by the path.
Teaching Approach
Electromagnetic Induction video lesson
Problem solving through game
– http://ia700204.us.archive.org/12/items/AP_Physics_B_Lesso
n_41/Container.html
Potential Student Difficulties
Confusion Between Electric Fields and
Magnetic Fields
– Magnetic Fields are typically introduced after Electric Fields
– Content is often on same test
– A force on a moving charge in an electric field is same direction as field line
at that point
– Force on a moving charge in a magnetic field is perpendicular to direction
of the field line at that point
– Students commonly apply principles of electric field to magnetic field
– Solution:
• Continually reemphasize the distinction between electric fields and
magnetic fields throughout the unit
• If the students have grasped the concept of forces on electric fields, it
may be helpful for them to remember the directions of forces in a
magnetic field using the right hand rule.
Safety Consideration
 Considering the nature of adolescents, they should be well monitored while they
are in the virtual lab activity in order to make sure that they are doing the job as
intended
 Unsafe websites should be blocked either by appropriate settings on browser or
through school’s server
 Students demonstrate that they have the knowledge, skills, and habits of mind
required for safe participation in science activities and laboratories when they
(Ontario Science Curriculum, 2008):
• maintain a well-organized and uncluttered work space;
• follow established safety procedures;
• identify possible safety concerns;
• suggest and implement appropriate safety procedures;
• carefully follow the instructions and example of the teacher;
• consistently show care and concern for their own safety and
that of others
Potential Student Difficulties
Visualizing and Understanding Magnetic
Field Lines
– How can student’s understand the properties of magnetic fields when they
cannot be seen or touched?
– Solution:
• Using iron filings, a bar magnet, and an overhead projector, project an
image of a magnetic field by sprinkling iron filings around a bar
magnet.
• Have the students conduct a hands on activity map out a magnetic
field surrounding a bar magnet using a compass . The compass
direction at each point mapped will indicate the direction of the
magnetic field line.
• Students will then be able to describe both the direction and strength of
a magnetic field surrounding a permanent magnet and predict and
sketch magnetic field lines.
Differentiated Assessment
Students would have a choice for their culminating task assessment on the concept of
magnetic field. The following tasks are targeted to students’ multiple intelligences:









A Cartoon as shown in the introduction of magnetic field ,They can convey any idea
about magnetic field(Visual)
A song about the earth’s magnetic field, examples are in YouTube(Musical)
A model showing the magnetic lines using iron fillings(Kinesthetic)
A videotaped conversation about any concept included in the magnetic field(Linguistic
group work)
A hand written magazine about the concept of magnetic field(Intrapersonal, Group
activity)
Design an experiment to investigate the magnetic field around two long parallel
conductors with equal currents in opposite directions. Assume the wires are very close
together and the measurements are taken from at least 5.0 cm away. (Logical)
Students’ understanding of the concepts of magnetic field would also be
evaluated on a unit test
Formative assessment would be completed based students contribution in assessment tool
in Gismo lesson plan and participation in the online lab.
Practical Applications
• Maglev Trains
– Trains that use electromagnetic propulsion to move via
temporary magnetic fields power by a large
electrical source.
– Rather than directly using fossil fuels, maglev trains
are powered by a combination of electric coils in the
guide way walls and track.
• Cellular Phone Radiation
– Electromagnetic fields emitted by electrical devices
including cellular phones are linked to childhood
cancers and Leukemia.
– How can we protect ourselves?