Chapter 25 lecture - Chapter 25 Current and Resistance...

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Unformatted text preview: Chapter 25 Current and Resistance (Electrodynamics) Exam Thursday in 4404 Randall at 6:30 pm No book or personal electronic devices Bring calculator, pencils, 1 formula card Mr. Watsoncome hereI want to see you What are these 2 items and how are they related? S. Morse in 1844 Al Bell in 1876 A little history early 1800scrude telegraphs 1837first commercial telegraph for railroad use 1844Samuel Morse public demo of telegraph 1866---Trans-atlantic telegraph cable 1876---Alexander G. Bells new telephone 1879---Thomas Edison caps 50 years of light bulb research 1882Edisons first electric power generating plant 1880sIndustry embraces electric lighting and motors 1889-92Edison-General Electric becomes G.E. 1899Trans-atlantic wireless signal Electric Current, I I = dQ/dt in Coulombs/s = Ampere (A) (direction convention is that of + charge flow) The actual flow direction of particles may be different from I: Semiconductors (electrons or + holes) Metals (electrons) Ionic solutions (+ or ions, or both) Salt water solution of Na and Cl DEMO Resistance, R Macroscopic definition: Apply potential difference V = V and measure I that flows: Define R: R = V/I in Volts/A = ohm, (omega) V Question #1: R may depend on which parameters?...
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Chapter 25 lecture - Chapter 25 Current and Resistance...

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