The net force on one of the charges due to other charges is F =
2kq2
a2
+
kq2
2a2
=
5
2
(
kq2
a2
) where k =
1
4πε
. Here, as shown in the figure, line AB divided the soap film into two equal parts. The free-body diagram of half part is also depicted in the figure here.
At equilibrium, the surface tension balances the force. Therefore, Fsurface = 2√2αγ That is, 2√2αγ =