The distance between charges +q and -q is 2l and between +2q and -2q is 4l. The electrostatic potential at point P at a distance r from center O is - [ qlr2 ] 109 V, where the value of is . (Use 14 0=9 109 Nm2C-2) [figure]
Answer
27
Solution
Two dipoles at O (dipole moment points from - to +):
q pair: p1=q(2l)=2ql towards +x
2q pair: p2=2q(4l)=8ql towards -x
pnet=8ql-2ql=6ql along -x, so angle between p and OP =180 -60 =120
V= kp r2= 9 109 6ql 120 r2
=-27 [ qlr2 ] 109 V
=27
Answer: 27