# Someone help explain electric dipole situation

• Captain Levi
In summary, electric dipoles are described by two opposite charges of equal magnitude, but this is not a definition. There is a theorem stating that the lowest multipole moment is independent of the origin, and for dipoles, this means that the dipole moment does not depend on the position of the charges. However, if the charges are not equal, the lowest moment does not vanish and the dipole moment will depend on the position of the charges. So, a charge distribution can have a dipole moment without being a dipole itself.
Captain Levi

Ok so she says that electric dipoles are of opposite charge but equal magnitude at 3:40. But then at 5:33 she shows 2Q with -Q, at that point the magnitude of the 2Q particle wouldn't be equal to the -Q so they wouldn't be electrical dipoles right?

Captain Levi said:
Ok so she says that electric dipoles are of opposite charge but equal magnitude at 3:40. But then at 5:33 she shows 2Q with -Q, at that point the magnitude of the 2Q particle wouldn't be equal to the -Q so they wouldn't be electrical dipoles right?
At 3:40, she gives an example of a dipole, not a definition. A dipole is described by two opposite charges, but not necessarily of the same magnitude.

berkeman and sophiecentaur
Captain Levi said:

Ok so she says that electric dipoles are of opposite charge but equal magnitude at 3:40. But then at 5:33 she shows 2Q with -Q, at that point the magnitude of the 2Q particle wouldn't be equal to the -Q so they wouldn't be electrical dipoles right?

Well, That is not really the way to look at it. First of all, there is a theorem that says the lowest nonvanishing multipole moment is independent of origin. The lowest multipole moment is just the total charge and if the charge configurtation contains equal and opposite charges, that vanishes. The next multipole is the dipole and with two equal and opposite charges, the "monopole" moment vanishes and therefore the dipole moment does not depend on how you choose your coodinates. Thst is what makes it a dipole and not just a charge distribution with a dipole moment. If they are not equal as in your example with charges 2Q and -Q, the lowest moment does not vanish because the total charge is Q, so there is a term proportional to Q and any dipole moment of the configuration depends on the position of the charges. You can have a charge distribution that has a dipole moment without the distribution itself being a dipole.

Last edited:

## 1. What is an electric dipole?

An electric dipole is a pair of equal and opposite charges that are separated by a small distance. This results in a dipole moment, which is a measure of the strength and direction of the electric dipole.

## 2. How does an electric dipole form?

An electric dipole can form when a neutral atom or molecule is slightly displaced from its equilibrium position, causing a separation of charges within the atom or molecule. It can also form when two equal and opposite charges are brought close together.

## 3. What is the significance of an electric dipole?

Electric dipoles are important in understanding the behavior of electric fields and their interactions with charged particles. They also play a crucial role in various phenomena such as polar molecules, capacitance, and dielectric materials.

## 4. How is the strength of an electric dipole measured?

The strength of an electric dipole is measured by its dipole moment, which is the product of the magnitude of the charges and the distance between them. The dipole moment is usually represented by the symbol "p" and has units of coulomb-meters (C⋅m).

## 5. Can an electric dipole be oriented in any direction?

Yes, an electric dipole can be oriented in any direction. The direction of the dipole moment is always from the negative charge to the positive charge, but the orientation of the dipole itself can be changed by rotating it around its center or by changing the direction of the electric field acting on it.

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