Unit VI: Electricity and Magnetism
Introduction
General Instructional Objectives (and corresponding Specific Learning Outcomes) | Unit Content |
Knows terms
Understands the meaning of terms |
charging by contact and induction, capacitor, conductor, insulator, semiconductor, superconductor, electrically polarized, electrostatics, electric field, electric potential, electric current, resistance, direct and alternating current (dc and ac), electric power, magnetic field, magnetic domains, electromagnets, electromagnetic induction, generator, transformer |
Understands scientific concepts | conservation of charge, electric potential energy, Coulomb's Law, Ohm's Law, direct and alternating current, series and parallel circuits, magnetic domains, electromagnets, magnetic force, Earth's magnetic field, Faraday's Law, Maxwell’s counterpart to Faraday’s Law |
Knows all laboratory procedures
Prepares a plan for an experiment Participates in classroom activities Respects the scientific process Displays a scientific attitude Demonstrates skills in laboratory work |
All content |
Instructional Foci
Electric current is the flow of charge. The flow of charge can be illustrated using a simple circuit. In exploring the simple circuit, voltage sources and resistance should be discussed. Then the relationship between the flow of charge (current), resistance, and voltage can be related using Ohm’s Law. You might ask students to think about why it is that a bird can sit on a wire of high potential and not be harmed (answer: no voltage difference between its legs). Direct current and alternating current should be defined. This should lead to a discussion of the speed and source of electrons in a circuit. For example, how is it that turning on a light switch almost instantaneously produces light? Do electrons flow that fast? The answer is that current is not literally electrons flowing, but, rather, it is the electric field (which travels at nearly the speed of light) established inside the conductor (wire) once the switch is flipped, which nudges the randomly moving electrons in the right direction. Now that students know how their household switches work, they should study how they are configured to work the way they do. Parallel and series circuits should be demonstrated.
The section on magnetism should begin with a discussion on magnetic forces, poles and fields. The teacher should demonstrate how like poles repel, and opposite poles attract and how magnetic fields behave using a magnet and iron filings. Placing unmagnetized iron near a magnet can magnetize it. In doing so, large clusters of randomly oriented atoms in the unmagnetized iron interact with the magnetized iron by lining up with each other. These large clusters are called magnetic domains. Students can actually listen to the magnetic domains aligning with an amplified stethoscope. Then the interaction between electric currents and magnetic fields, known as electromagnetism, should be discussed. Practical applications of this relationship such as doorbells and magnetically levitated trains should be discussed. In addition, magnetic force on moving charged particles and current-carrying wires should be studied. Using the right hand rule to determine the relationship between the vectors of the magnetic field, the force, and the direction of current should be demonstrated for the students. To conclude the section on magnetism, the earth’s magnetic field should be discussed. How the change in the magnetic field over time allows us to date oceanic sediments through geologic time should be presented. In addition, a discussion of aurora borealis and aurora austrealis would be interesting and appropriate.
The final section of the unit should begin by defining
and discussing electromagnetic induction, which is summarized by Faraday’s
law. Then the application of electromagnetic induction in a generator and
in a motor can be compared and contrasted. Nikola Tesla and George Westinghouse
put electromagnetic induction to use with a turbogenerator, used to generate
enough electricity to light entire cities. The teacher should then discuss
transformers and their application of electromagnetic induction. A precautionary
note about self-induction when using electromagnets would be appropriate
if the teacher intends the students to use any electromagnets. Finally,
the equal and opposite law of Faraday’s law, know as Maxwell’s counterpart
to Faraday’s law, should be studied.
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