Chapter 25 lecture

# Chapter 25 lecture - Chapter 25 Current and...

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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

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“Mr. Watson—come here—I 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 1800’s—crude telegraphs 1837—first commercial telegraph for railroad use 1844—Samuel Morse public demo of telegraph 1866---Trans-atlantic telegraph cable 1876---Alexander G. Bell’s new telephone 1879---Thomas Edison caps 50 years of light bulb research 1882—Edison’s first electric power generating plant 1880’s—Industry embraces electric lighting and motors 1889-92—Edison-General Electric becomes G.E. 1899—Trans-atlantic wireless signal

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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) DEMO
Resistance, R Macroscopic definition: Apply potential difference ΔV = V and measure I that flows: Define R: R = V/I in Volts/A = ohm, Ω (omega) V Question #1: R may depend on which parameters?

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• Fall '07
• Evrard
• Current, Resistance, Car battery, lead acid battery, typical flashlight battery

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