Question

If the force acting on a point charge kept on the axis of an electric dipole is F, what will be the amount of force if the distance of the point charge is doubled from the dipole?

(a) 2F

(b) \(\frac {F}{8}\)

(c) \(\frac {F}{2}\)

(d) \(\frac {F}{4}\)

I had been asked this question in quiz.

My question is from Electric Dipole in section Charges and Fields of Physics – Class 12

Answer 1

Right option is (b) \(\frac {F}{8}\)

Easiest explanation: If the distance of a point charge, kept on the axis of a dipole, is sufficiently large than the separation between the charges of a dipole, then it can be shown that electric field E at a distance r from the dipole varies as E α \(\frac {1}{r^3}\). Now if the distance becomes 2r, electric field intensity will decrease by a factor of 2^3=8 times. Therefore the force F will now become \(\frac {F}{8}\).