# What is an electric dipole?

Let’s continue the journey down the rabbit hole of electromagnetic physics to discuss something that straddles the line between chemistry and physics.

What is an electric dipole? Good question. An electric dipole is an object that has one electric point charge on one end and the opposite electric point charge on the other end. The most common example of this is the common water molecule. Hydrogen typically comes with an ionic charge of +1. Oxygen has an ionic charge of -2. This means that the oxygen end of the molecule will have a negative charge while the hydrogen pair end will have a positive charge. Because of this, water is a powerful solvent. Ionic compounds dissolve in water because of the ability of water to attract both the positive ions and negative ions of a given solute.

Objects that contain electric dipoles are subject to electromagnetic fields. These fields produce a torque upon the object. The torque, tau, is equal to:

$\tau = q * E * d* sin(\theta)$.

$\theta$ is the rotation required for the dipole to be in line with the field. The charge is represented as q. The electric field strength is represented as E and the distance between point charges in the dipole is represented as d.

We can also pull another equation out of that by taking the charge and multiplying it by the angular displacement required. That gets us our dipole moment which is a vector quantity. Throw it into i-j-k format and you can solve for torque by hand!

Just take the cross product of the dipole moment vector and the electric field strength vector. That will also be your torque! Ok, maybe it’s not that exciting but it might come in handy.

Did you know that aligning an ionic molecule requires work to be done? Yep, sure does.

Think about it. Rotating a water molecule causes force to act over a distance. Sounds pretty work-worthy to me.

To figure that bad boy out, take the definite integral from the ending angle ($\theta$2) to the starting angle ($\theta$1) of (-DipoleMoment*E*sin($\theta$)) $d\theta$

There’s your work done on the system. I think that covers most everything you might run into with electric dipoles. As always, if there are any questions feel free to email Wirebiters.com using the top link.