Find the electrostatic force between a proton and an electron in a hydrogen atom if their separation is 5.3 ´ 10^-11 m.  What does the sign tell you?                                                  

Formula first: F =  __1__ Q₁Q₂ (P)

                                       4pe₀      r²

F = 9 ´ 10⁹ m/F ´ +1.6 ´ 10^-19 C  ´ -1.6 ´ 10^-19 C (P)

                           (5.3 ´ 10^-11 m)²

F = - 8.20 ´ 10^-8 N (P)

The minus sign tells us that the forces are attractive. (P)