Dipole Moment

There are two kinds of charges. Positive charges and negative charges. The positive charges are caused due to an atom containing excess protons, the positively charged sub-particles of an atom.

The negative charges are caused due to excess electrons which are the fundamental sub-particles of an atom containing negative charges. 

The electric and the magnetic fields are caused due to these charges. The dipole moment occurs when such oppositely charged particles are separated from each other. The electric dipole moment is different from the magnetic dipole moment. The dipole moment measures the polarity of the bond.

Dipoles

Before we learn about the dipole moment, it is important to understand what a dipole is.

 There exists a pair of charges which are opposite in nature or a magnetised pole. The magnitude of these charges is equal. 

These oppositely charged particles or the magnetic poles are separated by a specific distance. All of this forms a dipole. The dipole is a concept of electromagnetism. Dipole moment is the property of these dipoles.

Types of Dipoles

The dipoles are of two types of dipoles based on whether they are electric in nature or magnetic in nature. Let’s take a look at them.

• Electric Dipole:

An electric dipole is formed when a positively charged particle is separated from the negatively charged particle in an electromagnetic system. 

For example, suppose a small positive charge is placed near a small positive charge separated by a very small distance. A dipole would exist in that system. Dipole could be temporary or permanent.

• Magnetic Dipole:

When an electric system is closely circulated, it leads to the formation of a magnetic dipole.

For example, a wire that has a constant flow of current is made into a loop. Then a magnetic dipole would be formed around the wire.

The magnetic dipole is also of temporary as well as permanent type. The above example is of a temporary dipole. 

An example of a permanent dipole moment is a bar magnet.

The Dipole Moment

The earth can be taken as an example of a dipole moment. The geographical north pole is near its south magnetic pole and the north magnetic pole of the earth is near its south geographical pole.

Both these poles are equal in magnitude and separated by the distance of the earth’s diameter.

But let’s see what exactly is a dipole moment.

The dipole moment characterises the electric and the dipoles. The dipole moment is a vector quantity. 

Electric Dipole Moment

For an electric dipole, the direction of the simple electric dipole moment points towards the positively charged particle from the negatively charged particle.

The magnitude of this electric dipole is equal to the product of the strength of both the charges with the distance that separates the opposite charges.

Magnetic Dipole Moment

The magnetic dipole moment is directed through the loop. The magnitude of the magnetic dipole moment is the product of the area of the loop and the current flowing through the loop. The right-hand grip rule is applied here.

Along with the magnetic materials, some fundamental particles, as well as the electric particles, exhibit the magnetic dipole moment.

An electron, which is the fundamental sub-particle of atoms and molecules, produces a magnetic dipole moment similar to that of a very small current loop.

The Dipole Moment Formula

As we discussed, the measure of dipole moment is obtained by multiplying the magnitude of the opposite charges and the distance of separation between those opposite charges. The Greek letter µ is used to denote the dipole moment.

The formula can be represented as given below.

Dipole moment = Charge × distance of separation

Symbolically, it can be represented as, 

µ = Q/r

The unit by which the dipole moment is measured is called the Debye unit. The Debye unit is denoted by “D.” 

The value of one Debye is equal to 3.33564 × 10-30 C.m.  Here, the m stands for Metre and C stands for Coulomb.

Another type of dipole moment is the bond dipole moment. Bond dipole moment exists between two atoms of opposite electronegativities.

The formula used to measure the bond dipole moment is given below.

μ = 𝛿.d

 Here, the μ is used to represent the bond dipole moment.

The 𝛿  is the magnitude of the partial negative and positive charges such as 

𝛿+ and 𝛿–.

The bond dipole moment is a vector in nature.

The direction of the bond dipole moment is parallel to the bond axis.

It starts with the positive charge and then ends with the negative charge.

So, to sum it up, the dipole moment exists between two equal and oppositely charged particles separated by a small distance.

Conclusion

When two oppositely charged particles with similar magnitude are placed at a small distance away from each other, then that results in the formation of a dipole. The dipoles are of two types: electric dipoles and magnetic dipoles.

The dipole is measured with the help of the dipole moment.

The formula to measure the dipole moment is Dipole moment = Charge × the distance of separation. The unit to measure the dipole moment is the Debye unit. The formula to calculate the electric dipole moment is different from the formula of the magnetic dipole moment. It is a vector quantity.