Prozorov_17 - PHYSICS 222 Introduction to Classical Physics...

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Unformatted text preview: PHYSICS 222 Introduction to Classical Physics II Prof. Ruslan Prozorov Iowa State University Fall 2011 LECTURE 17 Faraday’s law. Applications. Transformers. induced current PHYS222 - Lecture 17 - Prof. Ruslan Prozorov - Iowa State University 3 October 2011 2 magnetic flux PHYS222 - Lecture 17 - Prof. Ruslan Prozorov - Iowa State University 3 October 2011 3 emf and the current induced in a loop PHYS222 - Lecture 17 - Prof. Ruslan Prozorov - Iowa State University 3 October 2011 4 Find the direction of an induced emf PHYS222 - Lecture 17 - Prof. Ruslan Prozorov - Iowa State University 3 October 2011 5 Faraday’s law of induction The induced electromotive force (EMF) in any closed circuit is equal to the time rate of change of the magnetic flux through the circuit. it is closely related to the Maxwell equation: For a tightly-wound coil of wire, composed of N identical loops, each with the same flux ΦB, Faraday's law of induction states that PHYS222 - Lecture 17 - Prof. Ruslan Prozorov - Iowa State University 3 October 2011 6 Michal Faraday Faraday's big discovery happened in 1831 when he found that when you change a magnetic field, you can create an electric current. He did a lot of other work with electricity such as making generators and experimenting with electrochemistry and electrolysis. (22 September 1791 – 25 August 1867) Faraday's experiments started with magnetic fields that stayed the same. That setup did not induce current. It was only when he started to change the magnetic fields that the current and voltage were induced (created). He discovered that the changes in the magnetic field and the size of the field were related to the amount of current created. Scientists also use the term magnetic flux. PHYS222 - Lecture 17 - Prof. Ruslan Prozorov - Iowa State University 3 October 2011 7 Faraday’s law experiment A diagram of Faraday's iron ring apparatus. Change in the magnetic flux of the left coil induces a current in the right coil. PHYS222 - Lecture 17 - Prof. Ruslan Prozorov - Iowa State University 3 October 2011 8 alternating current PHYS222 - Lecture 17 - Prof. Ruslan Prozorov - Iowa State University 3 October 2011 9 an ac generator PHYS222 - Lecture 17 - Prof. Ruslan Prozorov - Iowa State University 3 October 2011 10 a rod moving in a uniform magnetic field PHYS222 - Lecture 17 - Prof. Ruslan Prozorov - Iowa State University 3 October 2011 11 generator - simplified PHYS222 - Lecture 17 - Prof. Ruslan Prozorov - Iowa State University 3 October 2011 12 work and power in a slidewire generator PHYS222 - Lecture 17 - Prof. Ruslan Prozorov - Iowa State University 3 October 2011 13 Lenz’s Law Induced electromotive force (emf) always gives rise to a current whose magnetic field opposes the original change in the magnetic flux PHYS222 - Lecture 17 - Prof. Ruslan Prozorov - Iowa State University 3 October 2011 14 The Faraday Disk dynamo PHYS222 - Lecture 17 - Prof. Ruslan Prozorov - Iowa State University 3 October 2011 15 wind turbine The first automatically operated wind turbine, built in Cleveland in 1887 by Charles F. Brush. It was 60 feet (18 m) tall, weighed 4 tons (3.6 metric tonnes) and powered a 12kW generator. PHYS222 - Lecture 17 - Prof. Ruslan Prozorov - Iowa State University 3 October 2011 16 transformers PHYS222 - Lecture 17 - Prof. Ruslan Prozorov - Iowa State University 3 October 2011 17 transformers • Another application for electromagnetic induction is the transformer. Transformers are used to either increase or decrease the magnitude of an alternating current. The structure of a transformer consists of two coils, called the primary and the secondary, linked by an iron core which is used to concentrate the magnetic field. When an alternating current is applied to the primary, it generates a magnetic field in the iron core the changing magnetic field induces an EMF in secondary coil. Depending on the ratio of turns in the primary coil to the secondary determines whether the transformer is a step-up or step-down. PHYS222 - Lecture 17 - Prof. Ruslan Prozorov - Iowa State University 3 October 2011 18 an ideal transformer d Vp N p dt d Vs N s dt Vp N p Vs N s incoming power = outgoing power: I pV p I sVs PHYS222 - Lecture 17 - Prof. Ruslan Prozorov - Iowa State University 3 October 2011 19 electric motors … PHYS222 - Lecture 17 - Prof. Ruslan Prozorov - Iowa State University 3 October 2011 20 AC and DC motors AC PHYS222 - Lecture 17 - Prof. Ruslan Prozorov - Iowa State University DC 3 October 2011 21 and generators PHYS222 - Lecture 17 - Prof. Ruslan Prozorov - Iowa State University 3 October 2011 22 energy conversion PHYS222 - Lecture 17 - Prof. Ruslan Prozorov - Iowa State University 3 October 2011 23 ...
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This note was uploaded on 11/14/2011 for the course PHYS 5863005 taught by Professor Meyer during the Fall '09 term at Iowa State.

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