By charge conservation,
Q¢  = Q/2 This implies V¢  = V/2 The total energy of the system is
6
1
1
2
'
'
2 25
10
J
2
4
Q V
QV
−
=
×
=
=
×
Thus in going from (a) to (b), though no charge is lost; the final
energy is only half the initial energy