Question

Use the worked example above to help you solve this problem. A 5.10-mu C point charge is at the origin, and a point charge q_2 = -1.70 mu C is on the x-axis at (3.00, 0) m, as shown in the figure. (a) If the electric potential is taken to be zero at infinity, find the electric potential due to these charges at point P with coordinates (0, 4.00) m. V (b) How much work is required to bring a third point charge of 3.70 mu C from infinity to P? J Suppose a charge of -1.70 mu C is at the origin and a charge of 3.20 mu C is at the point (0, 3.00) m. (a) Find the electric potential at (4.00, 0) m, assuming the electric potential is zero at infinity. V (b) Find the work necessary to bring a 3.70 mu C charge from infinity to the point (4.00, 0) m. J

Answer 1

a)

We solve this by using the principle of superposition. That is, we find the potential at point C by finding the potential at that point due to charge A alone, then finding the potential at that point due to charge B alone, and then simply adding them up. Because we are taking the potential to be zero at infinity, we can use the equation that the potential due to a point charge q that is a distance r away from that point charge

V = kq / r

The potential at point C due to the charge a point A is

VAC = (9 x 10^9 x 5.10 x 10^-6) / 4

VAC = 11475 volts

VBC = (9 x 10^9 x -1.7 x 10^-6) / 3

VBC = -5100 volts

Vtot = VAC + VBC

Vtot = 6375 volts

b)

W = q*Vtot

W = (3.7 x 10^-6 x 6375)

W = 2.3587 x 10^-2 J