Teaching the Concept of Magnetic Fields

1. Teaching the Concept of Magnetic Fields Daniele Cerone Jincy Binoy

2. Introduction to Magnetic Fields Is there ay special territory for a magnet in which the Iron Nail get attracted? Yes It has a magnetic field To be continued

3. 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.

4. 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

5. 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 current-carrying 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

6. Teaching Approach Magnetic Field A video demonstration http://www.youtube.com/watch? v=zbTrHWW3xvU

7. 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

8. 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 Gismos Magnetic Induction

9. Teaching Approach 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. 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 α I Ampere’s Law Power point presentation M(I/2 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. B=µ(I /2ПR)

10. Teaching Approach Electromagnetic Induction video lesson Problem solving through game • http://ia700204.us.archive.org/12/items/AP_Physics_B_Lesson_41/Container.html

11. 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.

12. 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

13. 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.

14. 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.

15. 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?