NOTES 28 - Topics 5 and 6 - Electricity

2. NOTES 28 - Topics 5 and 6 - Electricity ---------------------------------------------------------------------------------- 6.2.1 Electric Charge (q) - caused by the presence of charged particles; • On the atomic level, protons have q = +1e; electrons have q = -1e; (the charges, ie., positive and negative were named by Ben Franklin) • Matter is usually neutral, ie., q = 0, because the same number of protons and electrons are present; •On the macroscopic level (human scale), charge (q) is measured in Coulombs (C); 1.00 C = 6.25 x 1018 elementary charges • A “net charge” (ie., q > 0) results from an excess or shortage of electrons; protons are never gained or lost; 1p = proton; mp = 1.67 x 10-27 kg; 1 qp = +1.60 x 10-19 C mp = 1872me qp = -qe 0 e = electron; me = 9.11 x 10-31kg; -1 qe = -1.60 x 10-19 C • Opposite charges attract each other and like charges repel each other; - Charging by Friction- a neutral object is rubbed with another neutral object causing electrons to taken by one object and lost by the other; both objects become charged with equal and opposite charges (ie., conservation of charge); - Charging by Contact (aka Conduction) - a neutral object receives a charge by contact with a charged object when electrons are deposited or removed from it; - Charging by Induction (aka Electrostatic Induction) - the electrons in a neutral object are rearranged by the presence of a charged object so that the object acts as if it is charged even though it is still neutral;

3. 6.2.2 The Law of Conservation of Electric Charge- charge is neither created nor destroyed, but only rearranged; the net electric charge produced by any process is zero; 6.2.3 Conductors and Insulators • Conductors - materials which allow electrons to pass through and/or across easily; electron are not tightly bound to the nuclei; many “free electrons” are present; examples - metals and some metalloids; • Insulators - materials which allow few on no electrons to pass through and/or across; electrons bound tightly to the nuclei; virtually no “free electrons” present; examples - nonmetals and some metalloids; • Semi-Conductors - materials which, because of the presence of certain “impurities,” allow electrons to pass through and/or across; most electrons are bound tightly, but some electrons are allowed to pass through “holes” in the material; no free electrons present; example: Silicon + Germanium; Semi-Conductors http://www.national.com/kbase/category/Miscellaneous.html#6

4. • Superconductor - materials which act as moderate to good conductors under normal conditions, but become “perfect conductors” (ie., no resistance) at a particular temperature; Superconductors http://superconductors.org/ Type II Superconductors (all ceramics) Hg0.8Tl0.2Ba2Ca2Cu3O8.33......................................138 K* HgBa2Ca2Cu3O8......................................................133-135 K HgBa2Ca3Cu4O10.....................................................125-126 K HgBa2Ca-xSrxCu2O6................................................123-125 K HgBa2CuO4................................................................94-98 K (*current high-temperature record-holder)

5. What's my charge distribution?

15. Mini-Lab #14: Play with the electroscope and the electrophorus. On one side of your paper draw the charges on the electroscope when the foil tube is at an angle. On one side of the paper draw the motion of the charges in the electrophorous. What would make it have more force?