Four point charges are to be placed at the four corners of a square of side length
PHYSICS · Multi-part · A Level · Physics · Fields and their consequences · Fields and their consequences
Problem
Four point charges are to be placed at the four corners of a square of side length a. In Arrangement I each charge has value +q. In Arrangement II the charges are placed so that adjacent corners carry charges of opposite sign (that is, the sequence around the square is +q,−q,+q,−q).
Answer the following questions about the two arrangements.
(1) Describe qualitatively (no calculations required) how the net electric potential energy of Arrangement I compares with that of Arrangement II. In your discussion, comment on the relative magnitudes and signs of the two energies.
(2) State which arrangement would require an external agent to do greater positive work to assemble the charges from infinity, and explain your reasoning in terms of the interactions among the charges.