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Conceptual Physics Study Notes & Questions: Electromagnetics (Chap. 17) 1) Batteries work by chemical reactions that separate electrons from atoms, creating a difference in electric potential between the battery’s two terminals. (p354) 2) The motion of electric charge produces a magnetic field. This field circles around the electrons’ motion vector—such as in a wire—in a direction that can be described by the right hand rulethat is, point your right hand thumb in the direction of the electrons’ motion and the circulation direction of the generated magnetic field follows the bending direction of your right hand’s fingers. (p357) 3) Make a coil of conductive wire and flow an electric current through it. The generated magnetic field flows in a single direction through the center of the coil, exits at one end, curves around and re-enters through the opposite end of the coil. This is an electromagnet. There are no starting points for magnetic fields—they always form continuous loops. (p357) 4) Using the push/pull of interacting magnetic fields, permanent magnets, electromagnets, and AC (alternating) current, you can construct an electric motor. How does it work? (p358) 5) Conductive wires passing through a magnetic field will have an electric field induced in the wire, causing an electric current to flow. This is called electromagnetic induction and is the basis of an electric generator. (p365) An electric motor and generator are essentially the same device, the former converts electrical energy to work, the latter converts work to electrical energy. 6) Electromagnetic induction means that a changing magnetic field creates an electric field. A transformer is two loops of wire configured so that the magnetic field generated by one electromagnet will flow through the other coil (p387). Flowing an AC current through one coil will create a time-varying magnetic field. This changing magnetic field will induce an AC current in the second coil. The voltage across the first coil, compared to that induced in the second coil is equal to the number of coil windings in the first coil divided by the number of 1 windings in the 2nd coil. (p361) 7) Important note: When a changing magnetic field induces a current in a coil of wire, the direction of the induced current is generated such that the magnetic field produced in the coil is in the opposite direction of the original magnetic field. (p362) 8) Maxwell’s Equations describe the full interaction of electric and magnetic phenomena (p367): 1) there are electric point sources (electrons and protons); 2) there are no magnetic point sources—magnetic force lines always form continuous loops that curve back on themselves; 3) a changing electric field (e.g. moving electrons) creates a magnetic field; and 4) a changing magnetic field induces an electric field. 2