Given, q1=10µC=10−5C q2=12µC=1.2×10−5C r1=10cm=10−1m We have to find work done in bringing them Closer when, r2=6cm =6×10−2m Work done, W= change in potential energy in two configuration of charges =
1
4πε0
q1q2
r2
−
1
4πε0
⋅
q1q2
r1
=
1
4πε0
q1q2(
1
r2
−
1
r1
)
=9×109×10−5×1.2×10−5(
1
6×10−2
−
1
10−1
) =1.08(
100
6
−10)=(
40
6
)×1.08=7.2J
Which is nearest to 8.1J hence, option (a) is correct.