What is an Electric Dipole?
Before we start with the electric dipole moment we must understand what do we mean by the term dipole and dipole moment. An electric dipole is a pair of equal and opposite charges separated by a considerably short distance. In an electric dipole, the magnitude of both the charges will be the same, we can not consider a pair of two charges with different magnitudes.
Since an electric dipole is a pair of equal and opposite charges, therefore the total charge in an electric dipole will be zero. While studying electric dipole we should understand that the total charge of an electric dipole is zero does not mean that field of an electric dipole is zero.
Dipole Moment
Whenever two equal and opposite charges are brought together there will be either some attraction or repulsion force between them. Some examples of electric dipoles are HCl, H₂O, CH₃COOH, etc. These molecules will have fixed dipole moments because the center behavior center of the positive charge will not be coinciding with the negative charge. The electric dipole moment is a vector quantity, it has a specific direction and magnitude. The electric dipole moment physics plays an important role to understand the concept of polarisation. Now, let us define electric dipole moment, or in other words, let us have look at how do we define dipole moment of an electric dipole.
Define Electric Dipole Moment
Now, the dipole moment definition is given as the product of the magnitude of charges and the separation between them. The dipole moment determines the strength of an electric dipole to produce the electric field. It is denoted by P and it is a vector quantity.
Mathematically, the electric dipole moment is given by:
Consider two point charges q and -q place on dipole axis separated by a distance 2a, then the electric dipole moment is,
⇒ P = q x 2a………..(1)
Where,
q - The magnitude of the charge
2a - The separation between two charges
Equation (1) is known as the electric dipole moment formula physics.
The direction of the dipole moment is always from the negative charge to the positive charge. The SI unit of the electric dipole moment is Coloumb-meter(C-m). The dimensional formula of an electric dipole is
M⁰L¹T¹A¹
M⁰L¹T¹A¹.
Dipoles in an External Electric Field
Consider an electric dipole placed in an external electric field. The electric dipole will experience some force and is known as the torque. The torque is the force exerted on the dipoles placed in an external electric field and is given by,
⇒τ = P x E = PE Sin θ ………(1)
Where,
P - The dipole moment
E - The applied external field
Significance of Electric Dipole and the Electric Dipole Moment
The concept of an electric dipole is not only having importance in physics but it is an equally valid and prominent topic in chemistry as well.
We know that most of the matter made up of atoms and molecules will be electrically neutral. Depending upon the behaviour of the pair of charges, the molecules are subdivided into two types,
Polar Molecules: If the centre of mass of positive charge doesn’t coincide with the centre of mass of negative charge then it is known as a polar molecule.
Non-Polar Molecules: If the center of mass of positive charge coincides with the center, charges, s of negative charge then it is known as a Non-Polar molecule.
Polar molecules possess permanent dipole moments. These dipoles are randomly oriented in the absence of an external electric field. On applying an electric field, the polar molecules will align themselves in the direction of the electric field.
In a system, if the net charge is zero, that does not mean that there will be no electric field or the electric field will be absent. This was more evident by studying the electric dipole moment. Therefore, the study of an electric dipole is important.
The study of dipoles and the dipole moments will help us understand the concept of polarization.
Example
1. When an Electric Dipole P is Placed in a Uniform Electric Field E, at What Angle Between P and E the Value of Torque will be Maximum?
Ans: Given that an electric dipole is placed in a uniform electric field. We aim to calculate the maximum torque.
We know that the torque acting on a dipole placed in an external electric field is given by,
⇒τ = P x E = PE Sin θ ………(1)
Where, P - The dipole moment
E - The applied external field
Therefore, the value torque will be maximum when the angle between the electric field and the dipole moment is 90⁰
FAQs on Electric Dipole Moment
1. What is the difference between an electric dipole and an electric dipole moment?
An electric dipole is a separation of positive and negative charges. On the contrary; The electric dipole moment is the product of the magnitude of the charge and the distance between the centers of positive and negative charges. Although an electric dipole has the magnitude of its charge as q and its dipole moment is p. It is placed in uniform electric field E. Whereas considering this fact if its dipole moment is along the direction of the field the force on it and its potential energy are respectively.
2. What is the Direction of an Electric Dipole Moment?
The electric dipole moment is a vector quantity. Its direction is always considered from the negative charge to the positive charge.
3. What is the SI Unit of Electric Dipole Moment?
The SI unit of electric dipole moment is Coulomb meter and the dimensional formula is given by [M0 L1 T1 A1].
4. What is the use of an electric dipole?
Dipoles are usually found in molecular structures caused by the non-uniform charge distribution of protons and electrons. They are used to find the polarity of a system which is useful in understanding many chemical phenomena such as the normal force, surface tension, solubility.
5. How do you calculate the electric dipole moment of water?
As we know there are two hydrogens in water molecules and those two hydrogens create their dipole moments. Therefore, We have to calculate the individual dipole moments, and then we have to do the sum to get the dipole moment of the water molecule. Hence; the net dipole moment of the water molecule = 0.9187+0.9187=1.837D.
6. What is the application of Dipole Moment?
It is used for the calculation of the percentage ionic character, bond angle, electric polarization, and residual charge on the atoms in the molecules. It also helps to determine the size or shape of molecules and the arrangements of chemical bonds in the molecules.
7. What are the characteristics of a dipole?
The dipole is the simplest type of antenna from a theoretical point of view. Most commonly it consists of two conductors of equal length oriented end-to-end with the feedline connected between them. Dipoles are frequently used as resonant antennas. They are attractive forces between the positive end of one polar molecule and the negative end of another polar molecule.
