Concept PresentationElectromagnetic Induction

By: Benjamin Liu

Instructors: Marty Zatzman and Janine Extavour

What will be covered?• Basic review of key concepts that are

covered in electromagnetic induction• Key ministry expectations• Lesson sequence• Misconceptions with concepts in lessons• Different learning styles and approaches• Safety considerations• Practical Application• Useful resources

Anti-gravity and Levitation!

http://www.youtube.com/watch?v=eihdAHRH1Bc&feature=related

http://www.youtube.com/watch?v=WX1fkfJPWpY&feature=related

What the what!? That’s crazy!

Electromagnetic InductionThe Basics

• Faraday’s Law: As you move a closed-loop conductor (e.g. ring or solenoid) through a changing magnetic field (or vice-versa), you induce a current through the conductor.

• Oersted’s Principle: A conducting wire or solenoid with an electrical current will also generate its own induced magnetic field.

• Lenz’s Law: The induced magnetic field in a closed-loop conductor will oppose the change in the original magnetic field.

Activity!• Each table has piece of equipment

related to the aforementioned laws/principle

• Match yourself correctly with 2 other tables to put the full apparatus together.

• Play around! • Identify which aforementioned

law/principle this relates to, and explain how it works.

Ministry ExpectationsUnder Grade 11 University Physics: Electricity and Magnetism

F3.2 explain, 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

 F3.3 distinguish between conventional current and electron flow in relation to the left- and right-hand rules

F3.4 explain Ohm’s law, Kirchhoff’s laws, Oersted’s principle, the motor principle, Faraday’s law, and Lenz’s law in relation to electricity and magnetism

 F3.5 describe the production and interaction of magnetic fields, using diagrams and the principles of electromagnetism (e.g., Oersted’s principle, the motor principle, Faraday’s law, Lenz’s law)

Lesson Sequence

• Lesson #1 – Introduce Oersted’s principle, conventional current vs electron flow through a conducting wire and solenoid, and the right-hand and left-hand rules.  

• Lesson #2 – Introduce Faraday’s Law and Lenz’s Law, the interaction of magnetic fields, and forces on moving charges through a magnetic field.

 • Lessons #3 and #4 – Introduce the motor principle,

and practical applications of electromagnetic induction (e.g. motors, electrical generators, transformers).

Misconception #1There is only a left-hand/right-hand rule for

finding:a) Direction of magnetic field in a current-

carrying conducting wireb) Force exerted on a moving charge in a

magnetic field

Solution:Clarify that… Left-handed rules are used for electron flow, the movement of negative charges

ORRight-handed rules are used for conventional current, the movement of positive charges

• Left-hand rule(electron flow)

• Right-hand rule(conventional current)

Solution #1 (cont’d)

Misconception #2

A current is induced in a conducting wire by a static magnetic field

Solution:• Demonstrate Faraday’s experiment with the

students, showing them that the magnetic field must be constant flux to induce a current.

• Use the analogy: As you stand still in a swimming pool, you don’t feel anything. But, as you start to move, you start to create currents in the water.

Misconception #3The induced magnetic field produced in a conductor is equal in magnitude and direction to the change (flux) in the original magnetic field

Solution• Emphasize if the induced magnetic field was in the

same direction as the flux of the original magnetic field, a net amount of energy would be generated in the direction of change, which does not follow the conservation of energy.

• Demonstrate through actual demonstration (e.g. levitating coil) or by video demonstration.

Levitating coil: http://www.youtube.com/watch?v=4nTewAjhGsY

Lenz’s law app.: http://micro.magnet.fsu.edu/electromag/java/lenzlaw/

Teaching Different LearnersELLs

• They may already be familiar with the equipment and tools for electromagnetism from their respective countries, so bringing in equipment and tools, such as conducting wires, galvanometers, magnets, etc. to activate prior knowledge would be highly beneficial to them

• Have posters or designed posters by students to illustrate various ideas within electromagnetism, and place them around the room. They can be supplemented with words walls. Optional to keep these up during a test if assistance is to be given.

• Provide students with a list of words prior to the section, and can be given in a form of “foldables” which they can fill in with illustrations as they go along. Can also be used as an aide during tests.

Teaching Different Learners

Multiple Intelligences• Tactile – Bring in actual equipment and apparatus to

have students feel and try out, such as for Faraday’s experiment.

• Visual – Provide many diagrams, online videos, interactive applets, worksheets to create own representations of how electromagnetic field are induced, and forces on current-carrying conductors in magnetic fields

• Linguistic and Logical – Use many step-by-step detailed directions on how fields are generated. Supplemented with diagrams for visual learners.

• Interpersonal/Interpersonal – Working solo/pairs to solve problems in electromagnetic induction (e.g. what direction will the induced field be if the magnetic were brought closer into the conducting ring?)

Where in the curriculum?

Electricity and Magnetism should be taught as the or 5th and final unit Electromagnetism and

Electromagnetic induction is taught at the end of the unit• Brings together the ideas of energy, force,

motion, and waves. • Students will require experience within

visualizing concepts as well mathematical concepts prior to the unit

Safety Considerations

High(ish) voltage of power sources required for generating current flow through a conductor• Demonstrations will be the safest and most

controlled method of illustrating the concepts of electromagnetic induction.

• Most demonstrations are also very short in duration and will not be able to be substantial enough to be used as labs.

• If student volunteers are being used for the demonstrations, ensure that power sources are low voltage, or properly insulated.

Practical ApplicationElectrical generators

• As a turbine is spun through water-power, wind-power, etc., it turns a magnetic field through a conductor which induces an electric current, producing electrical energy.

Simple generator: http://www.youtube.com/watch?v=k7Sz8oT8ou0

Motors• The opposite of a generator where an electrical current is

sent through a conducting loop, which passes through a magnetic field which exerts a force on the loop.

Motor principle: http://library.thinkquest.org/27948/motor.htmlSimple motor: http://www.youtube.com/watch?v=it_Z7NdKgmY

Maglev trains

• An electric current is used to generate strong magnetic fields that create induced magnetic fields that suspend and move the trains with very little friction.

Maglev: http://www.youtube.com/watch?v=VuSrLvCVoVk&feature=relatedMaglev explanation:

http://www.phy.cuhk.edu.hk/phyworld/articles/maglev/maglev_e.html

Key ReferencesBrian Heimbecke et al., Physics Concepts and Connections Book Two: Teacher’s Resource Guide. 2002. Irwin Publishing. Toronto.

• An excellent resource guide providing lesson designs and flow, misconceptions, and designs of labs/demonstrations, and BLMs.

Ackroyd, J., et al. Physics: Level 30: Teacher’s Resource. 2007. Pearson. Canada.

• A good resource guide that provides the standard lesson design, preconceptions/misconceptions, BLMs, but also makes specific reference to pages in the corresponding text-book, as well as accomodations for multiple intelligences. An issue with this resource is that it is a bit disorganized.

 Hirsh, A. et al. Physics 11. 2002. Nelson. Toronto.

• An excellent text-book that provides detailed and step-by-step diagrams of the processes that occur in electromagnetic induction. Simple and logical flow of learning, as well as a lot of sectional questions to consolidate learning.

 Dick, G., et al. Physics 11. 2001. McGrawHill-Ryerson. Toronto.

• The pictures are not nearly as descriptive as the words. This is probably better for students who are more linguistic learners and for logical learners than it would be for the general visual learners. It goes a bit more in-depth than is necessary, and would act quite well as a teacher guide in learning the topic more clearly.

Davidson, M., Molecular Expressions. Interactive Java Applications. 2010. Florida State Univeristy. http://micro.magnet.fsu.edu/electromag/java/ . Used: July 9-11, 2010.

• This is an excellent website that deals with the concepts in electricity, magnetism, and electromagnetism. This URL, specifically, leads to many explanations of concepts and applets that allow visualization of the different laws in electricity, magnetism, and electromagnetism.