Four equal point charges q sit at the corners of a square of side d. The work needed to assemble this configuration from infinity is

1. Pairs: 4 sides at distance d (4 pairs) and 2 diagonals at distance d√2 (2 pairs). 2. Total PE = k q²[(4/d) + (2/(d√2))] = (k q²/d)(4 + 2/√2). 3. The work done from infinity equals this PE since the field at infinity does no work. _Source: syllabus Physics Part I, Ch 2 Example 2.4_