8/5/08Lecture 2 Part 11

8/5/08Lecture 2 Part 12 Electromagnetism 전자기학 Part 1 : Electromagnetic induction; Faraday’s Law Part 2 : Electromagnetic waves 전자 유도 전자기파

8/5/08Lecture 2 Part 13 Introduction Electricity E(x,t) and magnetism B(x,t) But also, the E and B fields affect each other; electricity and magnetism go together to make a unified interaction  electromagnetism

8/5/08Lecture 2 Part 14 The discovery of electromagnetic induction Electromagnetic induction was discovered independently by Michael Faraday (London) and Joseph Henry (Albany, NY) in 전자 유도 Faraday 1797 –1878 Henry

8/5/08Lecture 2 Part 15 Simplest demonstration of electromagnetic induction Observation: when the magnet moves, a current occurs in the coil of wire (measured by the galvanometer). Faraday developed many experiments to produce the effect, in different ways. Changing the magnetic field induces electric current in a nearby conductor.

8/5/08Lecture 2 Part 16 But the electric current is a secondary effect. The primary effect is an electric field. Electromagnetic induction is a field effect. When the magnetic field changes in time, there is an induced electric field. (If a conductor is present, then current is driven by the induced electric field.)

8/5/08Lecture 2 Part 17 Electromagnetic induction is a field effect.

8/5/08Lecture 2 Part 18 Faraday’s Law and Field Theory 장의 이론 Advanced Calculus!! 진보된 미적분학 Lenz’s Law: The induced current* opposes the change of magnetic flux. (*if a conductor is present) -- field theory--

8/5/08Lecture 2 Part 19 장의 이론 -- field theory-- Applications of electromagnetic induction ► self-inductance in an AC circuit

8/5/08Lecture 2 Part 110 Applications of electromagnetic induction ► the electric generator The design principle — how it works 전기 발전기 -- electric generator -- As the coil rotates, the flux  alternates, which induces an alternating emf around the coil.

8/5/08Lecture 2 Part 111 The electric generator — the practical device 전기 발전기 -- electric generator -- Torque must be applied to turn the rotating coil. Mechanical work is converted to electrical energy.

8/5/08Lecture 2 Part 112 Appliances hertz Transformers Mutual inductance, i.e., electromagnetic induction Transmission Lines 345,000 volts (AC) Power Plant Electric generators are driven by a primary energy source; e.g., Coal furnace Nuclear reactor Hydroelectric dam

8/5/08Lecture 2 Part 113 Applications of electromagnetic induction ► the transformer 변압기 -- transformer -- (1) Alternating flux is created here … (2) which makes an alternating flux here … (3) which makes and alternating emf here. Primary CoilSecondary Coil Iron Core (1) (2) (3)

8/5/08Lecture 2 Part 114 변압기 -- transformer -- Applications of electromagnetic induction ► the transformer

8/5/08Lecture 2 Part 115 electromagnetic induction Water flow drives the turbine Coal……………………………………… Petroleum or Natural Gas……… Nuclear Reactor…………………… Hydroelectric………………………… Percent used for electric power in USA 50 % 10 % 20% Primary Energy Sources

8/5/08Lecture 2 Part 116 Alternative Energy Sources ? renewable safe for the environment no carbon dioxide emission less expensive 양자택일 에너지원

8/5/08Lecture 2 Part 117 전기 발전기 -- electric generator -- The electric generator … the practical device

8/5/08Lecture 2 Part 118 Gangwon Wind Park in Korea

8/5/08Lecture 2 Part 119 Photovoltaic Solar Cells direct conversion from sunlight to electricity there is no mechanical generator