The lines show the equipotential contours in the plane of three point charges, Q

Question

The lines show the equipotential contours in the plane of three point charges, Q1, Q2, and Q3. The values of the potentials are in kV as indicated for the +5, 0, and -5 kV contours. The positions of the charges are indicated by the dots.

A.Calculate the work performed by an external agent to move a charge of -0.39x10-12C from `i' to `b'.

B.Calculate the magnitude of the electric field at `g' .

C.Calculate the magnitude of the force on a charge of 9.60E-19 C at `k'.

D.Calculate the magnitude of Q3. The magnitudes of the three charges are in the exact ratios of 1 to 2 to 3.

I have asked this question before and they keep getting it wrong! please help me to the right answer!

Explanation / Answer

a) from i to b is from +3 to -3 (kV) W = Q V = -6000 * -.39 * 10E-12 b) E = V / d = 2000 / .0093 using d as the distance between the 1000 V and -1000 equipotentials (my measurements will not be very accurate - use your diagram) c) Ek = 2000 / .0133 similar to (b) above F = E Q = Ek * 9.6 * 10E-19 d) Q3 > Q1 > Q2 (magnitude from diagram) Example: measure distance from charges to k on equipotential V = k Q2 (3 / 4.3 - 2 / 4.3 - 1 / 4.3) = 0 (using my units from screen) Do a similar calculation at say, the 5000 V equipotential Choose a point on the equipotential Then 5000 = k Q2 (3 / R3 - 2 / R1 - 1 / R2) Where you measure R1, R2, and R3 from each charge to that point and solve for Q2 and then Q3 = -3 * Q2

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