Chapter 15 - Electric forces & fields PHY232 – Spring...

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Unformatted text preview: Electric forces & fields PHY232 – Spring 2008 Jon Pumplin http://www.pa.msu.edu/~pumplin/phy232 (original ppt courtesy of Remco Zegers) PHY232 - Electric Forces & Fields 2 Electric Charges Two types of charge in atom: positive (carrier: proton ) negative (carrier: electron ) Nucleus consists of: Protons ( positive ) neutrons (neutral) Nucleus is surrounded by cloud of electrons ( negative ) If the atom is not ionized, it is neutral. By removing electrons, it becomes ionized and positively charged, since there are more protons than electrons Mass of the electron is much smaller than that of the proton or neutron m e =9.109x10-31 kg, m p =1.6726x10-27 kg PHY232 - Electric Forces & Fields 3 Question A neutral atom has b) more neutrons than protons c) more protons than electrons d) the same number of neutrons and protons e) the same number of protons and electrons f) the same number of neutrons, electrons and protons PHY232 - Electric Forces & Fields 4 Electric Forces Like charges repel each other. (A different “strong” force keeps the protons attached to their nucleus!) Unlike charges attract each other. (That’s what keeps the electrons attached to their atom!)-- + +- + PHY232 - Electric Forces & Fields 5 Conservation of charge In a closed system, charge is conserved . This means that charge is not ‘created’ but can be transferred from one object to another. Charge is quantized; there are only discrete amounts of charge. The electron carries one unit of negative charge (-e) and the proton carries one unit of positive charge (+e). 1e=1.602x10-19 C (Coulomb) PHY232 - Electric Forces & Fields 6 conductors In conductors (i.e., conducting materials) electric charge can move freely. The resistance to the flow of charge is very small. Example: metals like Copper; one of the electrons from each atom can move freely. PHY232 - Electric Forces & Fields 7 Conductors, Insulators & Semiconductors In conductors , charge can move freely - The resistance to flow of charge is very low. In insulators , charge cannot move freely - The resistance to flow of charge is very high. Semiconductors are materials whose properties are in between that of conductors and insulators (used in transistors)....
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This note was uploaded on 03/19/2008 for the course PHY 232 taught by Professor Mr.nagy during the Spring '06 term at Michigan State University.

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Chapter 15 - Electric forces & fields PHY232 – Spring...

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