SG_Chap15 - Chapter 15 Electric Forces and Electric Fields...

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Chapter 15 Electric Forces and Electric Fields We are all wired up • Send messages in your body • Use to monitor body – EKG • Use to manipulate body – Defibrillator – Tasers 15.1 Properties of electric charges Greeks (700 B.C. to 18 th century): existence of charges Franklin (~1750): two kinds of charges Two types: – Positive charge: protons (p = 1.60 x 10 -19 Coulomb ) • m p = 1.67 x 10 -27 kg ≈ m n (mass of neutron) – Negative charge: electrons (e = -1.60 x 10 -19 Coulomb ) • m e = 9.11 x 10 -31 kg IMPORTANT: 1. Like charges repel, unlike charges attract 2. Electric charge is always conserved If an electron is knocked out, the free electron will be negatively charged, and what is left will be positively charged. • Atoms are neutral • Positively charged central nucleus r~10 -15 m • Negatively charged electrons orbit r~10 -10 m
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Materials allowing charges to move freely: conductors – Typically metals (Copper, aluminum, silver, gold) – Power lines • Materials do not allow charge movement: insulators – Typically ceramics, dry wood, plastics – Handles for screw driver and pliers (electrical shocks are not pleasant) • Semiconductors: “chips” in computers, flash drives, LEDs and lasers (Silicon, Germanium)
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This note was uploaded on 03/30/2009 for the course PHY 102 taught by Professor Luo during the Spring '08 term at SUNY Buffalo.

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SG_Chap15 - Chapter 15 Electric Forces and Electric Fields...

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