Phys2212_L01 - Physics 2212 Electricity and Magnetism...

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Physics 2212 Electricity and Magnetism Lecture 1 Charge and Coulomb’s Law
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10/06/09 Physics 2212 - Lecture 1 2 This week week date Lecture topic Text reading tutorial lab 1 Aug 20 Charge and Coulombs Law 25.1 to 25.4 Charge Aug 25 Electric Field 25.5 to 26.1 Aug 27 Field Lines and Charge Distributions 26.2 to 26.3
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10/06/09 Physics 2212 - Lecture 1 3 The History of Electricity “Rub amber with wool, and it will pick up bits of wood, feathers, straw …” Thales of Miletus (640-546 BC) About 1736, Charles Francois du Fay (1698-1739) learned that rubbing glass and rubbing resinous substances (e.g., amber) seemed to produce charges of different kinds. He found that two charges of the same kind repelled each other, while two of unlike kinds attracted. He suggested that electricity might exist as two distinctly different types, which he named “vitreous” and “resinous” electricity . Electric elektron = Greek word for amber William Watson (1715-1790) suggested in 1746 that electricity was one “fluid” . One of the two kind of electricity proposed by Du Fay could be an excess ( + ) of this fluid and the other a difficiency of it ( - ). Flow from + to - could account for electrical discharge. Benjamin Franklin (1706-1790) adopted and popularized Watson's “one fluid” theory and chose vitreous e lectricity to be the positive type (thereby giving electrons a negative charge). Franklin’s great reputation won universal acceptance for this view.
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10/06/09 Physics 2212 - Lecture 1 4 Charging Experiments (1) Observations: 1. No force is observed between un-rubbed rods. 2. Plastic rods rubbed with wool repel each other. 3. Glass rod rubbed with silk attracts plastic rod rubbed with wool. 4. At increased distance, forces are decreased. 1 2 4 3
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10/06/09 Physics 2212 - Lecture 1 5 Charging Experiments (2) More Observations: 1. A (charged) plastic rod rubbed with wool attracts small pieces of paper. 2. A (charged) plastic rods rubbed with wool is attracted to an un-rubbed (neutral) plastic rod. 3. A plastic rod rubbed with wood is attracted to the wool, repelled by the silk. 4. No charged (rubbed) object attracts both the charged plastic rod and the charged glass rod. 1 2 3 4
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10/06/09 Physics 2212 - Lecture 1 6 Charging Experiments (3) Even More Observations: 1. The charge from a plastic rod rubbed with wool can be transferred to a metal sphere. 2. After the transfer, the plastic rod does not attract paper. 3. A 2
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Phys2212_L01 - Physics 2212 Electricity and Magnetism...

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