In the rectangle of the figure the sides have lengths 6.65 cm and 17.4 cm, q 1 =
ID: 2003766 • Letter: I
Question
In the rectangle of the figure the sides have lengths 6.65 cm and 17.4 cm, q1 = - 5.20 ?C, and q2 = + 2.20 ?C. With V=0 at infinity, what is the electric potential at (a) corner A and(b) corner B? (c) How much work is
required to move a charge q3=+3.13?C from B to A along a diagonal of the rectangle? (d) Does this work increase or decrease the electric potential energy of the three-charge system? Is more, less, or the same work required if q3 is moved along a path that is (e) inside the rectangle but not on a diagonal and (f) outside the rectangle?
Explanation / Answer
potential at a point due to a charge = k*q/r
so for corner A, potential due to q1 = -5.2*10-6*k/0.174 ; potential due to q2 = 2.2*10-6*k/0.0665
total potential = 28778 V
for corner B, potential due to q1 = -5.2*10-6*k/0.0665 ; potential due to q2 = 2.2*10-6*k/0.174
total potential = -589966 V
work done to move q3 from B to A = 3.13*10-6(589966 - 28778) = 1.75 Joules approx
work is done on the system, so it increases the potential energy of the system
the work done is independent of the path