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Unformatted text preview: 1 Lecture 3 Chapter 14. Matter & Electric Fields * Charged Particles * Electric Interactions between Charged Objects * Interaction of Charge & Neutral Matter Last Class: Dipole Moment Previously.Electric Fields E = 1 4 q 1 r 2 r Point charge: Dipole: for r>>s : E = 1 4 2 qs r 3 ,0,0 at <r,0,0> E = 1 4 qs r 3 ,0,0 at <0,r,0> +q-q s x y z at <0,0,r> E = 1 4 qs r 3 ,0,0 Dipole moment: Uniformly charged sphere: r r Q E sphere 4 1 2 = for r>R (outside) = sphere E for r<R (inside) p = q s Matter 1/18/11 4 Bohr Model Quantum Physics 2 Hydrogen atom: 1 proton, 1 electron If a Sodium atom (Na) loses an electron: Ordinary matter is electrically neutral. However, matter can be charged by adding/removing charged particles Net Charge Sodium atom: Sodium ion (Na + ): net charge = (+e) + (-e) = 0 http://static.howstuffworks.com/gif/ atom-quantum.jpg Conservation of Charge The net electric charge is conserved in any physical process. Charge can be transferred from one object to another. Annihilation : e + + e = + The net charge of a system plus its surroundings cannot change. http://svs.gsfc.nasa.gov/vis/a000000/a000100/a000182/a000182.mpg Pair production How a solid object becomes charged DEMO Plastic rod gets negatively charged when rubbed with fur....
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