EE2011 Engineering Electromagnetics EE2011 Engineering Electromagnetics(Semester I of Academic Year 2011/2012) (Semester I of Academic Year 2011/2012)Electric Fields NUS EE2011 Engineering Electromagnetics(Semester I of Academic Year 2011/2012) (Semester I of Academic Year 2011/2012)Prof Yeo Swee Pingeleyeosp@nus.edu.sgCoulombs Law Coulombs Lawquantitative observations (in free space) originally an empirical resultlater corroborated by further theoryrrq qF u 4202 1=rElectric Fields NUS EE2011 Engineering Electromagnetics 2later corroborated by further theory valid only for point charges(i.e. when r >> dimensions of q1and q2) formula for pair of charges extend via superposition for linear systemsCoulombs Law Coulombs Lawvectorial addition for (linear) assembly of point charges (attract for opposite polarity but repel for same polarity)total force on q1 q2F1F14F F F Fr r r r+ + =Electric Fields NUS EE2011 Engineering Electromagnetics 3for general N-charge assemblytotal force on qm +q1+q4q3F12F1314 13 12 1 F F F F + + =m nN1 nmn m== F Fr rElectric Field Electric Fieldnot convenient to employ for analytical formulationproceed by defining electric field due to charge q(a) place positive test charge qtestat point of interest(b) divide Coulomb force by qtestmagnitudeqrErFrElectric Fields NUS EE2011 Engineering Electromagnetics 4notes: qtest