A charge q that moves between two points A and B, and has an electric force acti

Question

A charge q that moves between two points A and B, and has an electric force acting on it ( and perhaps several other forces) has work W done on it by the electric force. The electrostatic force is conservative and so we can define a change in electric potential energy, . We defined electric field using the relation , and in a similar way we define electric potential commonly called voltage as delta V = W/q = (delta U)/q


A ball has mass 3.0 µg and charge -6 nC moves from point A to point B. It has the same speed at points A and B, and the work done by the electric field during the move is -1.7 mJ.
(a) What is the change in electric potential energy of the ball? 1
(b) What is the change in voltage between points A and B? 2
(c) At which point does the ball have a higher electric potential energy? 3 ---Select--- Point A Point B They have the same voltage There is not enough information
(d) Which point has the higher voltage? 4 ---Select--- Point A Point B They have the same voltage There is not enough information
(e) Has the kinetic energy of the ball changed?

Explanation / Answer

m = 3.0 µg, q = -6 nC, work done W = -1.7 mJ. (a) What is the change in electric potential energy of the ball? delta U = -W = 1.7 mJ (b) What is the change in voltage between points A and B? delta V = delta U/q = 1.7 mJ/(-6 nC) = -2.8*10^5 V (c) At which point does the ball have a higher electric potential energy? delta U = UB - UA > 0 so the ball has a higher electric potential energy at B (d) Which point has the higher voltage? delta V = VB - VA < 0 so the ball has a higher voltage at A (e) Has the kinetic energy of the ball changed? No, because the ball has same speed.

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