AP Physics B Objectives

Links:

College Board Topic III:
Electricity and Magnetism

Topics:

4. Magnetostatics
   1. Forces on moving charges in magnetic fields
   2. Forces on current-carrying wires in magnetic fields
   3. Fields of long current-carrying wires
5. Electromagnetic induction

Time Range:
5 weeks

Suggested Teaching Strategies:

• Illustrate magnetic fields by sprinkling iron filings around various magnets under transparencies on the overhead projector. Pass around 3D model to emphasize true field shape. Electromagnetic induction core lab will show how coil field resembles that of a bar magnet. Also use large battery-powered electromagnet to illustrate how it can be quite strong, turned on and off, etc.
• Teach the students the various Ampere hand rules (including straight wire and coil rules). Illustrate field around a wire using a compass.
• Teach Ampere's motor and generator rules. Apply the motor rule to speakers and show students a dissected speaker and one created with just a coil, magnet, and butter dish. Then show how a microphone is similar, and that a microphone can become a speaker and vice versa.
• Next use the motor rule to show how an analog meter works, using demonstration model and the large analog multimeter. Extend the meter behavior to how a motor works and show students how a motor is constructed and have them build one in their groups. (Sargent-Welch sells a nice cheap motor kit where students build field coil, armature, and commutator and run motor off a 1.5 V dry cell.)
• Then show how a generator is conceptually a motor used backwards and demonstrate concept with Genecon motor/generator. Discuss large-scale electricity generation and distribution, introducing transformers at that point. Demonstrate transformers by hooking up two coils with a common magnet, connecting one coil to large analog multimeter and other to battery with a hacksaw blade contact.
• Illustrate how a commercial generator avoids commutators and outputs AC for transformers. Demonstrate AC using party light demonstrator.

Aligned Resources:

• Core Lab 15: Magnetism
• Core Lab 16: Electromagnetic Induction
• Available magnetism demonstration equipment includes:
  • Bar and horseshoe magnets
  • Iron filings
  • 3D magnet model (transparent container with mineral oil and iron filings; small bar magnet slides into it)
  • Large battery-powered electromagnet (will hold several hundred pounds)
• Videotapes: Mechanical Universe - Magnetism (high school and college versions)
• Available electromagnetic demonstration equipment includes:
  • Large and small speakers, intact and dissected
  • Walkman radio with microphone in headphone jack
  • Large demonstration meter with exposed coil, removable horseshoe magnet, and battery connections
  • Large DC motor for 6V power supply
  • AC/DC motor/generator
  • AC/DC "Party Light" apparatus showing how a filament around a magnet behaves when AC vs. DC flows
  • Genecon motor/generator (with optional 1 farad capacitor)
  • Gilkey coils (useful for homemade speaker demo), hacksaw blade, batteries, wires, and large analog meter for transformer demo
• Electrical Power Generation PowerPoint (tour of Oologah power plant)

Revision Date:
December 2003