Question

Determine the magnitude of the force between an electric dipole with a dipole moment of 9 ✕ 10-29 C m and an electron. The electron is positioned

r = 28

nm from the centre of the dipole, along the dipole axis. Hint: Assume that

r >> d,

with d the charge separation distance in the dipole.

Answer 1

The magnitude of electric field along the dipole axis at distance r from its center, for small dipole (d<<r), is given by

$E=\frac{1}{4\pi\varepsilon_{o}}\frac{2p}{r^3}$

where p is dipole moment.

Magnitude of force on electron in electric field is given by

$F=eE$

Where $e=1.6\times 10^{-19}$ C is charge on electron.

$r=28nm=28\times10^{-9}m$

$F = (1.6\times10^{-19})\times(9\times10^9)\times\frac{2\times9\times10^{-29}}{(28\times10^{-9})^3}N$

$F = 1.8076\times10^{-14}N$