Transcription of Chapter 2 Electric Fields
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Chapter 2 Electric Fields
Chapter 2 Electric The Important The Electric FieldSuppose we have a point chargeq0located atrand a set ofexternalcharges conspire so asto exert a forceFon this charge. We can define theelectric fieldat the pointrby:E=Fq0( )The (vector) value of theEfield dependsonlyon the values and locations of the externalcharges, because from Coulomb s law the force on any test charge q0is proportional to thevalue of the charge. However to make this definition really kosher we have to stipulate thatthe test chargeq0is small ; otherwise its presence will significantly influence the locationsof the external Eq. around, we can say that if the Electric field atsome pointrhas the valueEthen asmallcharge placed atrwill experience a forceF=q0E( )The Electric field is avector. From Eq. we can see that its SI units must follows from Coulomb s law that the Electric field at pointrdue to a chargeqlocatedat the origin is given byE=kqr2 r( )where ris the unit vector which points in the same direction Electric Fields from Particular Charge Distributions Electric DipoleAnelectric dipoleis a pair of charges of opposite sign ( q) separated by a distancedwhich is usually meant to be small compared to the distance from the charges at which we1718 Chapter 2.
20 CHAPTER 2. ELECTRIC FIELDS mg F elec = qE E q = 24 mC Figure 2.2: Forces acting on the charged mass in Example 1. 1. An object having a net charge of 24µC is placed in a uniform electric field of 610 N C directed vertically. What is the mass of this object if it “floats” in the field? [Ser4 23-16] The forces acting on the mass are ...
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