What is the change of potential energy of a 3nC point charge when it is moved fr

Question

What is the change of potential energy of a 3nC point charge when it is moved from point A to point B in the figure Charges are given at two positions below. a) What is the electric field at x = 0 m? b) What is the electric potential DIFFERENCE between an initial point at x = 0mm and a point at x = + 1m? c) An electron is moved from the initial to final positions described in part b. What is the change in the electron's "electric potential energy"? Give your answer in both Joules and also electron Volts. Point charges, q = +46 nC and q = -75 nC, are placed as shown. In the figure, an external force transports an electron from point A to point B. What is the work done by the external force?

Explanation / Answer

Initial potential energy is U1 = k*q1*q2/r1 = (9*10^9*25*10^-9*3*10^-9)/0.05 = 1.35*10^-5 J

Final potential energy is U2 = k*q1*q2/r2= (9*10^9*25*10^-9*3*10^-9)/0.015 = 4.5*10^-5 J

change in potential energy is dU = U2- U1 = (4.5-1.35)*10^-5= 3.15*10^-5 J

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