lec21 - 21-1Physics IClass 21Thinking AboutElectric Fields...

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Unformatted text preview: 21-1Physics IClass 21Thinking AboutElectric Fields andElectric PotentialRev. 02-Apr-04 GB21-2Class #19Take-Away Concepts (Review)1.Electric field from point charge sources:(Total field is the superposition of point source fields.))r(rq41Ei2ii-=2.Force on a charge in an electric field:EqF=3.Electric field points away from + source charges.4.Electric field points toward source charges.21-3-+The Electric Field of a Point Charge (as a Source)The electric field is a vectorfield, meaning at each point inspace the electric field has a magnitudeand a direction. Weshow that by drawing arrows at representative points in thecorrect directions with lengths proportional to the magnitudes.Awayfrom positiveTowardnegativeJust because we dont draw an electric field vector ata point doesnt mean there is no electric field there.21-4Class #20Take-Away Concepts (Review)Physicist Generals Health Warning:Confusing electric potential (V) with electric potential energy(U) will be hazardous to your score on the next exam.1.Electric potential (V) and electric potential energy (U):VqU=2.Electric potential from point source charges:=iirq41V3.Relationship of electric field and electric potential.4.Electric field lines and equipotential lines.5.Calculating change in kinetic energy using electric potential.21-5Why do we solve problems like: Where is the Net E Field = 0?There are several problems in electromagnetic design where theobjective is to find a location where the electric (or magnetic) fieldhas specified properties, like being zero, constant, or similar.Examples range from electrostatic traps (for atoms, ions, or anti-matter) to magnetic resonance imaging systems.We pose problems like this in Physics I to give you the chance toexercise your knowledge of electric fields and electric potential.You need to keep clear in your mind which is a vector, which is ascalar, and how contributions add or subtract in different regions....
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This note was uploaded on 12/15/2010 for the course PHYS 0001 taught by Professor Nayak during the Spring '10 term at Rensselaer Polytechnic Institute.

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lec21 - 21-1Physics IClass 21Thinking AboutElectric Fields...

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