We are independent & ad-supported. We may earn a commission for purchases made through our links.
Advertiser Disclosure
Our website is an independent, advertising-supported platform. We provide our content free of charge to our readers, and to keep it that way, we rely on revenue generated through advertisements and affiliate partnerships. This means that when you click on certain links on our site and make a purchase, we may earn a commission. Learn more.
How We Make Money
We sustain our operations through affiliate commissions and advertising. If you click on an affiliate link and make a purchase, we may receive a commission from the merchant at no additional cost to you. We also display advertisements on our website, which help generate revenue to support our work and keep our content free for readers. Our editorial team operates independently of our advertising and affiliate partnerships to ensure that our content remains unbiased and focused on providing you with the best information and recommendations based on thorough research and honest evaluations. To remain transparent, we’ve provided a list of our current affiliate partners here.
Technology

Our Promise to you

Founded in 2002, our company has been a trusted resource for readers seeking informative and engaging content. Our dedication to quality remains unwavering—and will never change. We follow a strict editorial policy, ensuring that our content is authored by highly qualified professionals and edited by subject matter experts. This guarantees that everything we publish is objective, accurate, and trustworthy.

Over the years, we've refined our approach to cover a wide range of topics, providing readers with reliable and practical advice to enhance their knowledge and skills. That's why millions of readers turn to us each year. Join us in celebrating the joy of learning, guided by standards you can trust.

What Is a Dipole Moment?

By David Isaac Rudel
Updated: May 17, 2024
Views: 10,534
References
Share

A dipole is a neutral system comprising two oppositely-charged parts. For example, a water molecule is neutral as a whole, but one of its ends is positively-charged while the other is negatively-charged. Such an object can influence other charged objects through electromagnetic forces. The dipole moment of a dipole is a vector quantity describing the strength of this influence. Its size equals the magnitude of each charge, multiplied by the distance between the systems two parts.

The strength of the force exerted by a dipole on a distant particle can be approximated using the equation F=2*pkq/r3. Here, p is the dipole moment, k is Coulomb’s constant, q is size of the net charge on the distant particle, and r is the separation between the center of the dipole and the distant particle. This approximation is nearly perfect on the longitudinal axis of the system so long as r is significantly larger than the separation between the two components of the dipole. For particles far away from this axis, the approximation overestimates the force by as much as a factor of 2.

Einstein’s theory of relativity links electric forces to magnetic forces. The magnetic field of a bar magnet can be approximated by a dipole of magnetic charges, one near the north pole of the magnet, the other near the south pole. Such an assemblage is called a magnetic dipole and the influence it exerts on a distant charge moving perpendicular to the field can be approximated as 2*μqs/r3, where μ is the magnetic dipole moment and s is the speed.

An electric current moving in a circular wire generates a magnetic field similar to that of a short bar magnet. The magnetic dipole moment of such a wire has magnitude I*A, where I is the wire’s current and A is the area it traces out in space. At the atomic level, magnetism is often viewed as arising from the motion of electrons along curved paths. The size of the magnetic dipole moment for such a particle equals q*s/(2r), where q is the size of the charge, s is the speed of the particle, and r is the radius of the path.

In addition to quantifying the force of a dipole on distant charged particles, the dipole moment is useful for determining the force an external field exerts on a dipole. For example, a microwave oven creates short-lived, varying electric fields. These fields cause water molecules, which are electric dipoles, to spin. This rotational motion leads to rising temperature, which cooks the food. The maximum torque exerted on a dipole by an external field is simply the product of the dipole moment and the field strength.

Share
WiseGeek is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Link to Sources

Editors' Picks

Discussion Comments
Share
https://www.wisegeek.net/what-is-a-dipole-moment.htm
Copy this link
WiseGeek, in your inbox

Our latest articles, guides, and more, delivered daily.

WiseGeek, in your inbox

Our latest articles, guides, and more, delivered daily.