A uniform electric field of magnitude E=4.2N/C points, as illustrated in the fig

Question

A uniform electric field of magnitude E=4.2N/C points, as illustrated in the figure below, along the negative x axis. The x and y-coordinates of points A, B, and C are shown in the figure. Determine the differences in potential between (a) points A and B, points C and B, and points C and A. (b) What is the change in the potential electric energy of the system if a positive charge of 2nC is moved from B to C? How about from B to A? (c) What is the change in the potential energy if a negative charge of -2nC is moved from B to C? (d) How much work must be done to move the negative charge from B to C at constant speed?

Explanation / Answer

(a) VB - VA = 0 (since line joining A to B is perpendicular to Electric Field ) Answer

VB - VC = E x (4 - (-3) ) = 4.2 x 7 = 29.4 V Answer

VA - VC = VB - VC = E x (4 - (-3) ) = 4.2 x 7 = 29.4 V Answer

(b) Change in P.E. = Charge x P.D. = - 2 x 10-9 x 29.4 = -58.8 x 10-9 J Answer

For B to A, there is no change in P.E.

(C) Change in P.E. = -Charge x P.D. = 2 x 10-9 x 29.4 = 58.8 x 10-9 J Answer

(D) Work Done = Increase in P.E. = 58.8 x 10-9 J Answer

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