Transcript VIPP2A
8/5/08 Lecture 2 Part 1 1 Electromagnetism 전자기학 Part 1 : Electromagnetic induction; Faraday’s Law 전자 유도 Part 2 : Electromagnetic waves 전자기파 8/5/08 Lecture 2 Part 1 2 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 8/5/08 Lecture 2 Part 1 3 전자 유도 The discovery of electromagnetic induction Electromagnetic induction was discovered independently by Michael Faraday (London) and Joseph Henry (Albany, NY) in 1831. 1797 –1878 Faraday 1791 -1867 8/5/08 Lecture 2 Part 1 Henry 4 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. 8/5/08 Lecture 2 Part 1 5 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.) 8/5/08 Lecture 2 Part 1 6 Electromagnetic induction is a field effect. 8/5/08 Lecture 2 Part 1 7 Faraday’s Law and Field Theory 장의 이론 -- field theory-- d emf dt B E t Advanced Calculus!! 진보된 미적분학 Lenz’s Law: The induced current* opposes the change of magnetic flux. (*if a conductor is present) 8/5/08 Lecture 2 Part 1 8 Applications of electromagnetic induction ► self-inductance in an AC circuit 장의 이론 -- field theory-- R V /I L / I flux/curre nt emf L dI / dt dI V (t ) L RI (t ) dt 8/5/08 Lecture 2 Part 1 9 Applications of electromagnetic induction ► the electric generator 전기 발전기 -- electric generator -- The design principle — how it works As the coil rotates, the flux alternates, which induces an alternating emf around the coil. 8/5/08 Lecture 2 Part 1 10 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. 8/5/08 Lecture 2 Part 1 11 Appliances 120 volts @ 60 hertz 8/5/08 Transformers Mutual inductance, i.e., electromagnetic induction Transmission Lines 345,000 volts (AC) Lecture 2 Part 1 Power Plant Electric generators are driven by a primary energy source; e.g., •Coal furnace •Nuclear reactor •Hydroelectric dam 12 Applications of electromagnetic induction ► the transformer 변압기 -- transformer -- Primary Coil (1) Secondary Coil (2) (3) (1) Alternating flux is created here … (2) which makes an alternating flux here … (3) which makes and alternating emf here. 8/5/08 Lecture 2 Part 1 13 Applications of electromagnetic induction ► the transformer 변압기 -- transformer -- 8/5/08 Lecture 2 Part 1 14 electromagnetic induction Water flow drives 8/5/08the turbine Percent used for Primary Energy Sources electric power in USA Coal……………………………………… 50 % Petroleum or Natural Gas……… 10 % Nuclear Reactor…………………… 20% Hydroelectric………………………… 20% Lecture 2 Part 1 15 Alternative Energy Sources ? • renewable • safe for the environment • no carbon dioxide emission • less expensive 양자택일 에너지원 8/5/08 Lecture 2 Part 1 16 The electric generator … the practical device 8/5/08 Lecture 2 Part 1 전기 발전기 -- electric generator -- 17 Gangwon Wind Park in Korea 8/5/08 Lecture 2 Part 1 18 Photovoltaic Solar Cells • direct conversion from sunlight to electricity • there is no mechanical generator 8/5/08 Lecture 2 Part 1 19