Phy 103: Fundamentals of PhysicsElectromagnetic InductionFaraday’s LawGenerators & Alternating CurrentMichael Faraday (1791-1867)TransformersTransformers (cont.)Power TransmissionField InductionPhy 103: Fundamentals of PhysicsChapter 25: Electromagnetic InductionLecture NotesElectromagnetic InductionSo far we have observed that an electric current produces a magnetic fieldQuestion: Can a magnetic field produce an electric current?Answer: Yes!It’s called electromagnetic induction!!When a magnetic field is changed near a wire loop, a voltage (called electromotive force) is induced in the wireThe resulting voltage generates an electric currentThe size of the voltage depends on how fast you change the magnetic fieldThe size of the current depends on the resistance in the wire as well as the induced voltage (remember Ohm’s Law?)Faraday’s LawThe product of the area of a loop of wire (coil) times the magnetic field inside the wire is called the magnetic flux ( = B.AWhen the magnetic flux changes, a voltage is induced in the coil. The induced voltage (V) is related to:The number of loops (N) in the coilThe rate at which the magnetic flux is changing (/t) inside the loop(s), orNote: the magnetic flux changes when either the magnetic field (B) or the area (A) of the loop changes: = A.B or  = B.AtBANtNV)()( {Faraday’s Law}Generators & Alternating CurrentElectromagnetic induction can be used to produced electricityA device that does this is called an electrical generatorGenerators convert mechanical energy into electrical energyMechanical energy is utilized to either: rotate a magnet inside a wire coilRotate a wire coil inside a magnetic fieldIn both cases, the magnetic flux inside the coil changes producing an induced voltageAs the magnetic or coil rotates, it produces an alternating current (AC) {due to the changing orientation of the coil and the magnetic field}Types of generators:Turbine driven (turbo-) generatorsMagnetohydrodynamic generators (MHD)Michael Faraday (1791-1867)A self-trained English physicistPerhaps the greatest experimenter who ever livedNote: since he was self taught, he did not grasp mathematics!!!Major contributions to physics:Developed the concept of fields (electric and magnetic) or as he called them, “lines of force” invented the dynamo (a device capable of converting electricity to motion) discovered electromagnetic induction devised the laws of chemical electrodeposition of metals from solutionsTransformersDevises that utilize electromagnetic induction to increase or decrease the maximum voltage of an AC power sourceKey features:Primary coil (input): connects to AC power source & generates the magnetic fieldSecondary coil (output): connects to the “load circuit” & reacts to the magnetic field produced by primary coilRelationship between primary coil and secondary coil:where:V is the voltage of primary or secondary coilN is the number of coils in primary or secondary coilondaryondaryprimaryprimaryNVNVsecsecTransformers (cont.)Transformers obey conservation of energy law:Powerprimary = PowersecondaryPower input at primary coil will always be greater or equal to the power output at the secondary coilPower TransmissionTo transport electric power over large distances:voltages are stepped upCurrents are stepped downPower = Voltage x CurrentorP = V.ILower currents result in less power loss (due to heat)Transformers (at front end) are used to step up the voltage and lower currentTransformers (at back end) are used to step down the voltage and increase current for consumer usageField InductionFaraday’s Law in terms of fields:An electric field is induced in any region of space in which a magnetic field is changing with timeE ~ B/tThe direction of the electric field is at right angle to the changing magnetic fieldMaxwell’s counterpart to Faraday’s Law:A magnetic field is created in any region of space in which an electric field is changing with timeB ~ E/tThe direction of the magnetic field is at right angle to the changing electric