What Causes an Electric Dipole?

We are surrounded by electrical charges in our daily life. When you rub a comb over a towel and bring it close to your hair, a portion of your hair will cling to the comb. This is because of the electrical charge. Let’s look at how opposite charges behave when kept at a distance from each other. Electrostatics is a branch of physics that studies the electric dipole moment. A dipole is an electric charge separated by a distance ‘d’ from its opposite charge ‘q’. In space, electric dipoles are always moving towards the negative charge -q.

Electric Dipole Definition

Atoms with positive charges and molecules with negative charges are usually located simultaneously. As a result, they have zero dipole moment. Some examples include CO2 and CH4. Nevertheless, an electric field produces an electric dipole moment. On the other hand, the centres of negative and positive charges in some molecules are not precisely aligned. As a result, they maintain an electric dipole moment even without an electric field. This type of molecule is called a polar molecule. A good example of a polar molecule is water, or H2O. When subjected to an electric field, various materials show interesting properties and useful applications. 

Electric Dipole Moment

Electric dipole moment measures the separation of negative and positive charges within a system. In other words, it’s the overall polarity of a system. Coulomb meters (Cm) is the SI units for electric dipole moments. Physicists and chemists use another unit of measurement called ‘Debye’.

Electric dipoles are defined theoretically by the first-order term of a multipole expansion. They consist of two equal and opposite charges infinitesimally close to each other. Nonetheless, real dipoles do have separate charges. Electric dipole moments have equal and opposite charges. There is a distance ‘2a’ between the two charges(q) called dipole length. The charge and dipole centre are separated by the length ‘a’. What exactly is an electric dipole moment? μ = q.2a is the symbol for dipole moment, which can be termed a vector. The magnitude of this quantity is equal to either charge’s magnitude due to the lack of a sign specification for the dipole moment. 

Electric Dipole Direction

Dipole moment is the charge of any dipole multiplied by the distance between the two charges. So a dipole moment is a charge to estimate the distance between two charges. A dipole moment usually points in the same direction as the surrounding electric field, or a vector.

Ideal Electric Dipole

As q increases in magnitude and 2a decreases in the distance, we get an ideal dipole or point dipole. The product P* = q.(2a) is the dipole moment. If the magnitude of charge q increases, and the distance 2a decreases, we also obtain a point dipole or ideal dipole. Some protein molecules behave as ideal electric dipoles. 

Electric Dipole Significance

Dipole moments are vectors created when the magnitude of the charge is multiplied by the displacement vector pointing from the negative to the positive charge. Dipoles consist of two equal-magnitude charges with opposite signs.

A net-neutral system can be measured by its polarity/polarisation. Electric dipole moments are small when the separation between the charges is small, or the charges are small. The polarisation will result in a small electric field. If the polarisation is large, there will be a distinct non-monopolistic electric field (large charges/large separations).

The dipole moment is also a measure of an electric field’s tendency to align with a dipole. In a weak dipole, the moment will be parallel to the local field. External work like mechanical vibration or thermal effects do not prevent it from being twisted out of alignment.

Conclusion

The electric dipole moment of a polar molecule is permanent. When there is no external electric field, the dipoles are oriented randomly. A system’s net charge does not necessarily mean that there will be no electric field or that there will be no electric field when an electric field is applied. Polar molecules align towards the electric field in response to it. An electric dipole moment shows this more clearly. It is important to understand the concept of polarisation by studying electric dipoles and their moments.