Two fixed point charges are positioned on the x–axis: a charge at and a charge at
PHYSICS · Multi-part · A Level · Physics · Fields and their consequences · Fields and their consequences
Problem
Two fixed point charges are positioned on the x–axis: a charge +Q at (−d,0) and a charge −2Q at (+d,0). A small positive test charge q0 is released from rest at the point (0,3d) in the xy–plane. Neglect all forces other than those due to the two fixed charges.
(a) On a set of coordinate axes that you draw, sketch the initial direction of the acceleration of the test charge. Clearly label the axes and the three charge locations.
(b) At the instant of release, rank the magnitudes of the individual electric forces exerted on the test charge by the two fixed charges. Justify your ranking qualitatively in terms of both charge magnitude and separation distance.
(c) Describe qualitatively how the speed of the test charge changes as it moves, and explain your answer in terms of energy considerations.
(d) Suppose instead that the test charge were negative while all other aspects of the setup remain unchanged. Discuss how each of the following would be affected: (i) the initial direction of acceleration, and (ii) the ranking requested in part (b). Provide reasoning for each.