Unit VI: Electricity and Magnetism

Introduction

Only do we realize how important electricity is to our daily functions when it unexpectedly goes off. And a related phenomena to electricity is magnetism. They combine to form one of the four fundamental forces, electromagnetic force. In this unit there are four sections: electrostatics, electric current, magnetism, and electromagnetic induction. Covering these topics should take about 3 weeks. Intended Learning Outcomes
 
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

Experiments: static electricity, series and parallel circuits, magnetic fields; demonstrations: charging by friction—use rabbit fur to charge a rubber rod and styrofoam to charge plastic strips, charging by induction—use insulated metal spheres to induce charge on plastic rod, balloon sticks to wall due to polarization, hair standing on end using a Van de Graaff generator, simple circuit, magnets with iron filings, listening to magnetic domains align using an amplified stethoscope; homework—make a citrus cell (battery) using a paper clip, a copper wire, and a lemon, quizzes, class discussion, questions for thought from the Flying Circus of Physics Teaching Strategies To begin the study of electrostatics, electrical forces and electric charges should be discussed and demonstrated. The demonstration uses rabbit fur to induce a charge on a rubber rod. In addition, styrofoam is used to induce a charge on a plastic strip. The charged objects are then brought near uncharged object to observe the phenomena of electric forces and electric charges. This demonstration can also be used to show the basic concept derived from Coulomb’s Law. Then the teacher could try to charge a metal rod while holding it to introduce conductors, semiconductors, and insulators (the metal rod will not hold a charge because it is a conductor, so the charge will flow right into you). In addition, this demonstration along with the Van de Graaff demonstration can be used to illustrate the different means of charging an object: charging by contact (friction) and charging by induction. Charging by induction using the Van de Graaff generator can also be used to demonstrate charge polarization in insulators. Charging a balloon by contact and sticking it to a wall is another example of polarization. Then the teacher should study the forces that exist between things that are not in contact—electric fields. They should discuss electric shielding and electric potential. Then the teacher can refer back to the Van de Graaff generator as one device for storing electric energy along with capacitors.

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.
 

Special Notes
  1. All labs should be preceded by an in class demonstration by the teacher of the proper procedures. After viewing the demonstration, students’ homework should be to prepare a plan for the experiment. Due to the time constraints of high school classes it is imperative that students have thought through the experiment before class. You, the teacher, need to know that they are aware of proper equipment set-up and safety precautions as well as appropriate hypothesis development, variable controls, and observation and measurement procedures.
  1. Labs can be found in Laboratory Manual in Conceptual Physics by Bill Tillery.


return to main page
return to conceptual physics curriculum
return to astromath