Physics 213 General PhysicsSlide 2Slide 3Slide 4Slide 5Coulombs force and electric fields.Direction of Electric FieldDirection of Electric Field, contSlide 9Rules for Drawing Electric Field LinesElectric Field Line PatternsSlide 12Slide 13Slide 14Electric Field PatternsPhysics 213General PhysicsLecture 202 Last Meeting: Coulomb’s Law, Electric Forces Today: Electric Field, Gauss's Law3Q4Faraday introduced electric field and electric field lines which are said to exist in the region of space around a charged object. When another charged object enters this electric field, the field exerts a force on the second charged object2| ( ) |qE r kr=vr5Coulombs force and electric fields.1222112ˆrrqqkF 1222112ˆrrqqkF 12211ˆrrqkE q1q2qtestq3q4Superposition Principle7Direction of Electric FieldThe electric field produced by a negative charge is directed toward the chargeA positive test charge would be attracted to the negative source charge8Direction of Electric Field, contThe electric field produced by a positive charge is directed away from the chargeA positive test charge would be repelled from the positive source charge9An electron traveling horizontally enters a region where a uniform electric field is directed upward.What is the direction of the force exerted on the electron once it has entered the field?(a) to the left(b) to the right(c) upward(d) Downward(e) out of the page, toward the readerAnswer: dQuestion:Rules for Drawing Electric Field Lines1. The lines for a group of charges must begin on positive charges and end on negative chargesIn the case of an excess of charge, some lines will begin or end infinitely far away2. The number of lines drawn leaving a positive charge or ending on a negative charge is proportional to the magnitude of the charge3. No two field lines can cross each otherElectric Field Line PatternsPoint chargeThe lines radiate equally in all directionsFor a positive source charge, the lines will radiate outwardElectric Field Line PatternsFor a negative source charge, the lines will point inwardElectric Field Line PatternsAn electric dipole consists of two equal and opposite chargesThe high density of lines between the charges indicates the strong electric field in this regionElectric Field Line PatternsTwo equal but like point charges At a great distance from the charges, the field would be approximately that of a single charge of 2qThe bulging out of the field lines between the charges indicates the repulsion between the chargesThe low field lines between the charges indicates a weak field in this regionElectric Field PatternsUnequal and unlike chargesNote that two lines leave the +2q charge for each line that terminates on
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