Question

Two protons and an electron are assembled along a line, as shown above. The distance between the electron and each proton is a. What is the work done by an external force in assembling this configuration of charges?

(A) –2ke²/a 

(B) –3ke²/2a 

(C) ke²/2a 

(D) 3ke²/2a 

(E) 3ke²/a

Answer 1

The correct option is: (B) –3ke²/2a 

Explanation:

The work to assemble the charges is the potential energy of the system, which is the sum of the potential energies of each pair of charges U_E = –ke²/a – ke²/a + ke²/2a.