76. At a distance of r1 = 4 cm from an infinitely long charged thread there is a point charge q = 0.66 nC. Under the action of the field, the charge approaches the filament up to a distance of r2 = 2 cm, and work A = 50 erg is performed. Find the linear charge density τ?

Detailed solution. Decorated in Microsoft Word 2003. (Target decided to use formula editor)