Wisconsin, PHYS 202

Excerpt: ... Physics 202, Lecture 15 Todays Topics Faradays Law (Ch 31) Review Emf Change of Magnetic Flux and Emf () Lenz s Lenzs Law and its applications Formulation of Faradays Law Expected Preview: Ch 31.1-3 Sources of E and B Fields: An overview Sources for the electric field: Electric charges (Coulomb's Law, static) subjects of past several weeks Change of B field (Faraday's Law, varying in time) Today Sources for the magnetic field: Electric current (Biot-Savart Law/Amperes Law, static) Last week Change of E field (Ampere-Maxwell Law, varying) Ch 34 All these features are summarized in Maxwells Equations. Ch 34 Review: Electromotive Force (emf, ) Electromotive force , emf, is a measure of the voltage that can be provided by a source. emf is not a force, it has a unit of volts sources of emf: chemical process (battery) change of magnetic flux = 1.5V semiconductors. + + Demo: Emf and Change of Magnetic Flux e.g. battery: notice that emf has a direction emf may exis ...

Rowan, ENG 102

Excerpt: ... Freshman Engineering Clinic II OHM: The Man, The Law, The Field Lecture 2 Ohm: The Man, The Law, The Field Ohm: The Man Ohm, Georg Simon (1787-1854), German physicist, best known for his research on electrical currents. He was born in Erlangen and educated at the University of Erlangen. From 1833 to 1849 he was director of the Polytechnic Institute of Nrnberg, and from 1852 until his death he was professor of experimental physics at the University of Munich. His formulation of the relationship between current, electromotive force , and resistance, known as Ohm's law, is the basic law of current flow. The unit of electrical resistance was named the ohm in his honor. Microsoft Encarta Reference Library 2002. 1993-2001 Microsoft Corporation. All rights reserved. Ohm: The LawResistance A conductor allows an electric current to flow through it, but it does not permit the current to flow with perfect freedom. Collisions between the electrons and the atoms of the conductor interfere with the flow of electr ...

Weber, PHSX 2220

Excerpt: ... Physics 2220 (Schroeder) fall 2005 Name Problem Set 7 (due Friday, October 12) 1. You have a loop of wire and a bar magnet. List at least three different ways to change the magnetic flux through your loop (and hence to induce a current in it). For each way of changing the flux, explain whether the force that causes the electrons to flow around the wire is an electric force or a magnetic force. The figure below shows a triangular loop of wire that is being pushed with speed |v| into a magnetic field. Left of the dashed line, there is a uniform field B pointing into the page; right of the dashed line there is no magnetic field. The left end of the triangle enters the field at time t = 0. Use the magnetic force law (not the flux rule or Faraday's law) to compute the electromotive force in the loop. (Remember that electromotive force is the work per unit charge done on each moving electron, not counting any possible resistive forces in the wire. You can compute the work as FB ds, where ds is the displacement ...

UIllinois, ECE 329

Excerpt: ... ECE-329 Fall 2008 Homework 3 (Solution) September 15, 2008 1. In this problem, we will study Faradays law, d E dl = B dS, dt C which states that the electromotive force E = C E dl around any closed loop C equals the time rate of change of the magnetic ux B = S B dS through the surface S bounded by the loop. (a) If B = 0 at all times, the magnetic ux is also zero (B = 0), and therefore, according to Faradays law, the electromotive force is zero (E = 0) over any closed loop C. (b) If B =0 then it is possible for E = 0 if the path C is disturbed or being displaced in such a way that the magnetic ux B = S B dS varies in time. (c) Let us dene a closed loop C passing through the xed points P1 and P2 (see the next gure). dl path A P2 C dl P1 path B S Since B is time-independent, the corresponding magnetic ux B is also time independent, and therefore, dB E dl = = 0. dt C Breaking the closed path integral into two parts, we have ...

Syracuse, PHY 344

Excerpt: ... Feb. 2001 Magnetic Effects in Matter Phy 344 Introduction: This experiment is primarily intended to familiarize you with three important topics in magnetism: Electromagnets based on iron. Magnetic fluxmeters based on Faraday's law. The Hall effect in semiconductors. Each of these three topics will require that you understand a different type of physics. For electromagnets you generalize the basic idea that currents generate magnet fields to include the effects of strongly magnetic materials - in this case "soft" (ie. magnetically soft) iron. The fluxmeter is a device which measures magnetic flux by exploiting Faraday's law: a coil which cuts magnetic field lines will generate an electromotive force . Finally the Hall effect pertains to to the motions of the mobile charges inside matter when they experience both electric and magnetic forces. Suggested Reading: 1. Jerry B. Marion and William F. Hornyak, Principles of Physics (Saunders, New York, 1984), sections 31-4, 31-5, and Enrichment Topic B. This textboo ...

St. Lawrence, IT 308

Excerpt: ... ndreds of times larger than it would be for similar nonmagnetic metals. CLASS 20: ELECTROMOTIVE FORCE : The book talks about Electromotive force and its various causes, but there is not a lot here worth spending a lot of time with. The main thing I want you to see is that the Electromotive force , or "Emf" (normally pronounced "E-M-F"), is a voltage, not a force. Maybe the best thing to do is to write Emf, but pronounce it "oomf". I call it oomf because it is what provides the oomf to cause the charges to move in a circuit. OK, so in summary, Emf = voltage. The author's main reason for making a big point of the Emf seems to me to prepare you for the fact that there can be a nonzero Emf around a circuit. This contradicts Kirchhoff's voltage rule only if you confuse Emfs with voltages (which is a better thing to confuse them with than say 'forces'). MOTIONAL EMF: Let's return to the Hall effect. In the Hall effect a charge moving in a magnetic field is deflected, and this gives rise to a voltage perpendicular to ...

E. Michigan, PHY 222

Excerpt: ... circuits Ammeters and Voltmeters Specific Objectives This section, chapter 21 and the lectures that go with it, is the most important in our study of electricity because it provides the foundation for instrumentation in electrical measurements. Everything in this section is important, but you should pay particular attention to being able to: 1. understand the concept of electromotive force . 2. to use Ohm's law to help define resistance and to find the resistance in simple circuits. 3. differentiate between electric current and electron current. 4. calculate the power used in a circuit. 5. calculate the heat given off by a resistor in a given circuit. 6. calculate resistivity and demonstrate an understanding of this property. 7. demonstrate an understanding of what is meant by a semiconductor, and a superconductor. 8. define these terms: EMF resistance ohm watt kilowatt-hour resistivity superconductivity semiconductor 9. find the equivalent resistance for resistors in series and parallel circuits. 10. fin ...

Clark Atlanta, PHY 122

Excerpt: ... Class Notes 8 Instructor: H. L. Neal 1 Electromotive Force Electromotive force (emf) is de.ned as the amount of energy gained per unit charge that passes through a device in the opposite direction to the electric .eld produced by that device. It is measured in volts. Sources of emf include electric generators (both alternating current and direct current types) and batteries. Electromotive force is often denoted by E. + R Created using UNREGISTERED Top Draw 3.10 Oct 7,'106 3:17:27 PM E In the circuit Fig. 1, the emf prodiced by the battery pushes electric charge aroubd the circuit to produce the current I. The electric potential dierence accross the resistor is V = IR = E: 2 Resistors in Series and Parallel = R1 R2 R1 + R2 R1 = 1/R1 + 1/R2 R2 Createdu gUNREG ERED T pDraw3.10O 7,'106 2:46:58PM sin IST o ct The resistors add and resistors in parallel divide is a good way to remember how to determine the equivalent resistance for any combination. Note that this es exactly opposite to the rule fo ...

St. Mary MD, PHYS 2520

Excerpt: ... Lecture #26, March 20 Kirchhoff's Rules Today we shall continue our study of electric currents. In order to have electric current, it is necessary to have a closed circuit which starts at one of the terminals of the battery, connected to one or combination of electric devices and then connected to the other terminal of the battery. The battery serves as a source of energy for the circuit. If there is no current going through the battery then the potential difference across the battery is the same as its nominal value, which is also known as electromotive force of the battery . Knowing the electromotive force of all the batteries in the circuit, one can calculate currents in various parts of the circuit. These currents are related to potential drops according to the Ohm's law as I= V . Req (26.1) Here Req is the equivalent resistance for the appropriate part of the circuit. Last time our task was to find out how one can calculate this resistance for different combinations of the resistors. We shall continue ...

University of Texas, PHY 303l

Excerpt: ... s. You should read the first 3 sections of chapter 28 before coming to class. Class notes are available for Fridays lecture on current, resistivity, and resistance. Chapter 27 Currents and Ohms Law 27.1 Electric current 27.2 Resistance and Ohms Law 27.3 Resistivity of materials 27.4 Resistances in combination Chapter 28 Direct Current Circuits 28.1 Electromotive force 28.2 Sources of electromotive force 28.3 Single-loop circuits 28.4 Multiloop circuits 28.5 Energy in circuits; joule heat 28.6 Electrical measurements 28.7 The RC circuit 28.8 The hazards of electric currents ...