Moving Charges Around W5D3First Things FirstPoint ChargesGet to WorkSlide 5Slide 6What is the Potential Energy of q’?REMEMBERUNITS OF POTENTIALEquipotential LinesRelationshipQuestion: A 2C charge of mass m is released from point B and arrives at the equipotential G. How fast is it moving when it gets there?The three charges in the diagram are at the vertices of an isosceles triangle. Calculate the electric potential at the midpoint of the base, taking q = 7.00 μC.Example: Find potential at PSlide 15Slide 16Moving Charges Around Moving Charges Around W5D3W5D3Potential CalculationsSeptember 24, 2010First Things FirstFirst Things FirstQq=1 Coulomb0 r infinityPoint ChargesPoint Charges++Get to WorkGet to Workqq’IMPORTANT RESULTThe potential energy U of a system consisting of two charges q and q’ separated by a distance r Is given by:This also applies to multiple charges.rqqkU'What is the Potential Energy of q’?3'32211''rqkrqqkrqqkUqUnit is JOULESREMEMBERqFE •Just as the ELECTRIC FIELD was defined as the FORCE per UNIT CHARGE:We define ELECTRICAL POTENTIAL as the POTENTIAL ENERGY PER UNIT CHARGE:qUV VECTORSCALARUNITS OF POTENTIALVOLTCo ulombJoulesqUV Equipotential LinesRelationshipV V+VqEXWorkW q VW F X qE Xq V qE XVEX= D= D =- DD =- DD=-DQuestion: A 2C charge of mass m is released from point B and arrives at the equipotential G. How fast is it moving when it gets there?The three charges in the diagram are at the vertices of an isosceles triangle. Calculate the electric potential at the midpoint of the base, taking q = 7.00 μC.Example: Find potential at PmdrmdqqqqrV919.023.1)(14143210q1 q2q3 q4drPq1=12nC q2=-24nC q3=31nC q4=17nC q=36 x 10-9CV=350 Volts (check the arithmetic!!)Derive an expression in terms of q2/a for the work required to set up the four-charge configuration in the figure, assuming the charges are initially infinitely far apart.1234aadiagonal 71.12
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