Question

1. Point charges q1 = −4.5 nC and q2 = +4.5 nC are separated by 3.1 mm, forming an electric

dipole. (a) Find the electric dipole moment (magnitude and direction). (b) The charges are in a

uniform electric field whose direction makes an angle of 36.9 ̊ with the line connecting the charges.

What is the magnitude of this field if the torque exerted on the dipole has a magnitude 7.2 × 10−9N ∙

m?

Answer 1

Answer

Charge

$| q_1|=|q_2|=4.5nC.$

Distance d=3.1mm

a) electric dipole

$P=qd\\=4.5nC\times3.1mm\\=13.95\times10^{-12}C-m$

Direction is charge q₁ to q_2.

b) now electric field is given

$E=\frac{\tau }{P\sin\theta}$

Putting all values

$E=\frac{7.2\times10^{-9}}{13.95\times10^{-12}\sin36.9°}$

$=\frac{7200}{13.95\times.596}$

$=867.85V/m$