Three point charges are placed at the vertices of an equilateral triangle of side…
PHYSICS · Multi-part · A Level · Physics · Fields and their consequences · Fields and their consequences
Problem
Three point charges are placed at the vertices of an equilateral triangle of side L lying in a horizontal plane.
• Configuration I: All three charges are +Q.
• Configuration II: Two of the charges are +Q and the third is −Q (located at the apex).
Assume no other charges or fields are present.
(1) For Configuration I, show symbolically that the total electric potential energy can be written as UI=3kQ2/L. Outline the reasoning rather than performing a full numerical calculation.
(2) Without further calculation, determine whether the magnitude of the total electric potential energy for Configuration II is greater than, less than, or equal to that of Configuration I. Also state the sign of UII. Justify both conclusions by examining the contributing charge pairs.
(3) Suppose the side length is doubled to 2L while the charge values remain the same for Configuration II. Explain how UII changes in magnitude and sign.