Electromagnetism

Lecture 2 Part 1

Electromagnetism 전자기학 Part 1 : Electromagnetic induction; Faraday’s Law Part 2 : Electromagnetic waves 전자 유도 전자기파 Lecture 2 Part 1

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 Lecture 2 Part 1

1797 –1878 Faraday 1791 -1867 Henry 전자 유도 The discovery of electromagnetic induction Electromagnetic induction was discovered independently by Michael Faraday (London) and Joseph Henry (Albany, NY) in 1831. Lecture 2 Part 1

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. Lecture 2 Part 1

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.) Lecture 2 Part 1

Electromagnetic induction is a field effect. Lecture 2 Part 1

Faraday’s Law and Field Theory 장의 이론 -- field theory-- 진보된 미적분학 Advanced Calculus!! Lenz’s Law: The induced current* opposes the change of magnetic flux. (*if a conductor is present) Lecture 2 Part 1

Applications of electromagnetic induction ► self-inductance in an AC circuit 장의 이론 -- field theory-- Lecture 2 Part 1

Applications of electromagnetic induction ► the electric generator 전기 발전기 -- electric generator -- The design principle — how it works As the coil rotates, the flux F alternates, which induces an alternating emf around the coil. Lecture 2 Part 1

전기 발전기 The electric generator — the practical device -- electric generator -- Torque must be applied to turn the rotating coil. Mechanical work is converted to electrical energy. Lecture 2 Part 1

Power Plant • Electric generators are driven by a primary energy source; e.g., • Coal furnace • Nuclear reactor • Hydroelectric dam Transformers Mutual inductance, i.e., electromagnetic induction Transmission Lines 345,000 volts (AC) Appliances 120 volts @ 60 hertz Lecture 2 Part 1

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

Applications of electromagnetic induction ► the transformer 변압기 -- transformer -- Lecture 2 Part 1

electromagnetic induction Percent used for electric power in USA 50 % 10 % 20% 20% Primary Energy Sources Coal……………………………………… Petroleum or Natural Gas……… Nuclear Reactor…………………… Hydroelectric………………………… Water flow drives the turbine Lecture 2 Part 1

Alternative Energy Sources ? • renewable • safe for the environment • no carbon dioxide emission • less expensive 양자택일 에너지원 Lecture 2 Part 1

전기 발전기 The electric generator … the practical device -- electric generator -- Lecture 2 Part 1

Gangwon Wind Park in Korea Lecture 2 Part 1

Photovoltaic Solar Cells • direct conversion from sunlight to electricity • there is no mechanical generator Lecture 2 Part 1

Electromagnetism