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This 15 page Class Notes was uploaded by Kenneth Streich on Monday September 28, 2015. The Class Notes belongs to PHYS151 at University of Pennsylvania taught by Staff in Fall. Since its upload, it has received 19 views. For similar materials see /class/215423/phys151-university-of-pennsylvania in Physics 2 at University of Pennsylvania.
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Date Created: 09/28/15
Physics 151 Electric Charde Coulomb s Law of Force Electric Fields Gauss s Law Electric Potenial Capicitance Electric Current Conductors DC Electric Circuits Madnetic Fields Biot Savart Law and Ampere 8 Law Inductance and Faraday s Law Electromadnetic Waves Propagation Interference a Diffraction Electric Charge Experimental findings Exists in two forms called positive and negative by Benjamin Franklin in 1700 s Like charges repel Unlike charges attract Charge is conserved in a closed system Charge is quantized Natural unit is charge on electron e 160x10 19 Coulomb C First constituent of atom to be isolated in 1897 by JJ Thomson Electron charge is negative e Proton charge is positive e Note both conductors and insulators can be charged Conductor charge is free to move throughout this material Insulator charge is locked in place in this material Coulomb s Law of Force Describes electric force F between two point charges q1 and q2 separated by a distance r12 in a vacuum Experimental findings Magnitude of force is proportional to the product of the charges and inversely proportional to the square of the separation Direction of forces the two charges exert on each other is always along the line joining them Forces are e ual in ma nitude and oosite in direction Units F in Newtons N l t in Coulombs C l r in Meters m k9x10g Nm2C392 6 141t 20 10702 a x 39A Always remember Iquot 5 39 V to convert units Qi W3 Vim cm 10392 m 4 ll 10 10760 c nC 109 c Principle of Superposition What happens when there are more than two charges present Experiments show that the force on any charge is the vector sum of the Coulomb forces from each of the other charges This is called the principle of superposition This figure shows direction y of force from q1 on Q 39 NOW YOU can do any ql 20 MC Can you draw direction of electrostatics force from q2 on Q problem where you Can you draw direction of know the location of 55031 reSUItant force all the charges Read 21 121 3 Do homework exercises from section 213 Do you understand Polarization How does a comb charged by brushing your hair pick up uncharged pieces of paper Do you think the sign of the comb s charge matters Induction Why was the coke can attracted to both positive and negative rods What happens to the leaves of an uncharged electroscope when a positive rod is held near by Draw force vectors on each charge with length proportional to the size of the force 0 exalt a force on chargd body E A is formey posmnn as P DA 3 point P E is m force per unil c by A on a 65 charg ul barge mm P What are some other fields Temperature is a scalar field it has a magnitude at each point in space but no associated direction Wind speed is a vector field it has a magnitude and a direction o 2 4 6 so 1714 16 18 0 ms 0 5 10 15 10 15 30 35 40 5 111111 Electric Field Calculations Learning Objectives To use thedprinciple of superposition to calculate the electric fiel of multiple point charges and of continuous distributions of charge To learn the electric fields of common charge distributions Dipole Point charge Line of charge Ring of charge Sheet of charge Two oppositely charged sheets To study the motion of charged particles and dipoles in simple electric fields Electric Field Calculations How to tackle them Draw a picture Choose an element of charge dQ where you can write down the electric field dE Usually choose a point charge Any symmetries Replace dQ with an equivalent expression involving a charge density and a small geometric quantity that describes the shape of charge element dQ Choose coordinate to use for integration variable All angles and distances must be expressed in terms of the integration variable Look at limiting cases does your answer make sense 3 Line of Charge Ring of Charge Disk of Charge 115 X Problem 2196 A small sphere with mass m carries a positive charge q and is attached to one end of a silk fiber of length L The other end of the silk fiber is attached to a large vertical insulating sheet that has a positive surface charge density 6 When the sphere is in equilibrium what is the angle the fiber makes with the sheet dl v 12 Wuwommmzmm n mWmenwmv Summary Configuration Er Er Dipole i Old i r3 271780 r3 1 q 1 Ponnt r2 4780 r2 lnfinite line i 1 i r 2780 r Infinite sheet constant 2i 80 We ve covered everything in chapter 21 except for 216 On Friday we will move onto chapter 22 and learn about electric fields electric flux and Gauss s Law
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