An Overview of the Electric Dipole Moment is a Vector Quantity

Electric dipoles refer to a pair of equal and opposite charges separated by some distance. Electric dipole moment is the product of the magnitude of charges with the distance of separation between them. The electric dipole moment is a vector quantity (having both magnitude and direction) and has a defined direction that goes from negative charge to positive charge. The midpoint of these two equal and opposite charges is the centre of dipole where both the charges meet. These charges are equal and opposite, therefore they cancel out each other and the net charge thereafter becomes zero. 

Here’s more on the significance of the electric dipole moment. 

Electric Dipole Moment

The electric dipole being the pair of equal and opposite charges, its dipole moment is the product of the magnitude of these charges with the distance of separation. The electric dipole moment is a vector quantity and the formula for the electric dipole moment will be as follows:

p= q. d

Where q= magnitude of charge and d= distance of separation between these two charges. 

Dipole in an Electric Field

Although, the force cancels out each other as they are equal and opposite. However, they do still act as separate points, causing the development of torque in the dipole. 

Torque: The amount of force that can cause an object to rotate on its own axis is termed torque. Moreover, torque is responsible for causing the object to acquire angular acceleration whereas force causes it to accelerate in linear kinematics. It is also vector quantity and its direction is based on the direction of force acting on it.

Torque is represented by the symbol ‘τ’ which is pronounced as ‘tau’.

The formula for calculating torque is as follows:

Torque (τ) =Force × distance (separating the forces)

The formula for evaluating the magnitude of the torque will be as follows:

T = F r sinθ

Here, F – force, r -Arm length (temporary) and θ – Angle formed between the force vector and temporary arm.

The Significance of Electric Dipole:

The electric dipole holds great importance in both physics and chemistry. As we know that matter comprises molecules and atoms and these atoms consist of equal and opposite charges. The study of dipoles helps in getting a clear knowledge of concepts of polarisation. Based on the behaviour of these charges, the molecules are classified into two categories:

The electric dipole has great significance in physics and also in chemistry. The matter composed of atoms and molecules is usually electrically neutral. Thus, based on the behaviour of the pair of charges, these molecules are of two categories:

• Polar-Molecules: The centre of mass of positive and negative charge does not coincide with one another in the polar molecules. Moreover, they possess permanent dipole moments. In the absence of an electric field, they remain randomly oriented. However, on applying an electric field these molecules get aligned towards the direction of the electric field. 
• Non-Polar Molecules: Non-polar molecules are contrasting polar molecules and in these molecules, the centre of mass of negative and positive charges does coincide with one another.

Solved Questions on Electric Dipole Moment

Q 1- A uniform electric field of magnitude 2 × 105 N/C consists of a gas sample. Determine the maximum torque if the dipole moment of each molecule of this gam sample is 1.2 × 104 C-m. 

Solution:

The maximum amount of torque is when the angle formed is 90 degrees. Therefore, we will take the value of θ as 90 degrees.

Using the formula of torque, we get:

τmax = pE sin 90 

τmax = 2 × 105 × 1.2 × 104

τmax = 2.4×109 N-m

Q 2- A dipole has two equal and opposite charges i.e. +4 and -4C respectively. These charges have a distance of separation of 6 cm. Determine the dipole moment for these charges using the formula of dipole moment.  

Solution:

According to the data given in question:

q= 4 C

d= 6cm 

=0.06m

Using the formula of electric dipole moment, 

p= q×d

p= 4 × 0.06

p= 0.24 C-m

Answer: The dipole moment for these charges will be 0.24 C-m. 

Conclusion

Electric dipole moment is calculated by multiplying the magnitude of charges with the distance of separation between them. The electric dipole moment is a vector quantity and the direction is always from the negative charge to the positive charge. These charges are equal and opposite and cancel out each other making the net charge zero. The midpoint of these charges is the centre of charge and the line along the direction of an electric dipole is called the axis of the dipole. The electric dipole holds great importance in both physics and chemistry. The amount of force that can cause an object to rotate on its own axis is termed torque.