First Long ExamSecond Semester, AY 2016–2017Physics 7217.TriCharge.Three charges, coming from infinity, are placed on the corners of an equilateraltriangle with a side of lengthd. If two of the charges are+qand one charge is-q, howmuch work by an external force is required to assemble them?
18.Think about your X.Three charges are on the cornersof a rectangle as shown. What is the value of the electricpotential at point X?A.-9.00×103VB.-8.55×103VC.-7.11×103VD.+1.30×104VSolution:V=Xikqiri=k-10×10-95×10-2+-30×10-93×10-2+10×10-94×10-2=-8.55×103Nm/C(1)other choices: magnitudes only1.30×104Nm/Cdiagonal is 25cm-7.11×103Nm/Ccharges with equal magnitude contribute zero
19.Four You, I’ll Change.In a region of space, the electric potential is given byV(x, y) =4 exp(x-y). What is the electric field due to this electric potential?