×

Torque on Dipole

Top
Download PDF
FAQ

Bookmark added to your notes.
View Notes
×

The term dipole: in science is indeed a very mysterious word and doesn’t stop to surprise us as and when different topics are discussed. We are already familiar with the fact that the charge exists around us and along with their existence its presence leads to several natural phenomena as well. In addition, we can say that the positive and negative charges are present in different forms that showcase diverse properties in the attendance of a motivating field.

Have we ever heard about the concept of an electric dipole or dipole? This unique setup of electric charges that is the positive & negative charges does form an interesting concept of physics. In this article we are going to discuss the topic dipole in bread. To be precise there is an Electric Dipole that can be tagged as a separation between positive and negative charges.


Torque on a Dipole in a Uniform Electric Field

Before we understand the properties which are of the torque that is acting on an electric dipole in a uniform electric field. First of all let us brush up our understanding of torque and electric dipole very clearly.

The torque:

It is said to be the measure of force that causes an object to rotate about an axis is called torque. The term that is torque is a vector quantity and its direction generally depends on the direction of the force on the axis. The magnitude which is of the torque vector is said to be calculated as follows:

As : τ=FrsinΘ

where the letter r is called as the length of the moment arm and symbol θ is the angle between the moment arm and the force vector.

[Image will be Uploaded Soon]


Torque on Electric Dipole

A pair of charges which are electric that too with an equal magnitude but opposite charges usually separated by a distance d is known as an electric dipole as per definition. The dipole or the electric dipole moment for this is defined as the product of the magnitude of these charges and the distance which is between them. The moment of the electric dipole is a vector having a defined direction from the negative charge to the positive charge.  

That is given as p→=qd→

The torque on an Electric Dipole in an Electric Field that is uniform.

Now we consider a dipole with charges that is +q and –q which is forming a dipole since they are a distance d away from each other. Now let it be placed in a uniform electric field which is of strength denoted as E such that the axis of the dipole forms an angle θ with the electric field.

An electric dipole in an electric field that is external is subjected to a torque written as τ = pE sin θ where symbol θ is the angle which is between p and E. The torque tends to align the moment of the dipole p in the direction of E. The potential energy which is of the dipole is given by the symbol Ue = −pE cos θ or in the vector notation that is Ue = −p · E. 


Torque on Dipole in  Electric Field That is Uniform

                                                 [Image will be Uploaded Soon]

Now let us consider a dipole with charges that are +q and –q forming a dipole since they are a distance denoted by letter d that is away from each other. Let it be placed in a uniform electric field which is of strength denoted by E. In such a manner that the axis of the dipole forms an angle that is θ with the electric field.

  • Now the measure of force that causes an object to totally rotate about an axis is called a torque.

  • There is a pair of electric charges with an equal magnitude but opposite charges that are separated by a distance ‘d‘ is called an electric dipole.

  • Since there is the force magnitudes which are equal and are separated by a distance d the torque on the dipole is given by the following

Torque (τ) = Force × distance separating forces

The term dipoles whether they are electric or magnetic can be characterized by their dipole moment which is a vector quantity. For the simple electric dipole we can say that the electric dipole moment points from the negative charge towards the positive charge and has a magnitude that is equal to the strength of each charge times the separation between the charges. To be precise: we can understand it as for the definition of the dipole moment one should always consider the "dipole limit" where for example there is  the distance of the generating charges that should converge to 0. 

The moment of electric dipole is a measure of the separation of positive and negative electrical charges within a system. That is said t o be the  measure of the system's overall polarity. The SI units for the moment of the electric dipole are coulomb-meter (C⋅m). However a very commonly used unit in atomic physics and chemistry is the debye denoted as D.

Theoretically we can say that an electric dipole is defined by the first-order term of the multipole expansion; it consists of two opposite and equal charges that are infinitesimally close together. Although the diapoles really have separated charges. However we will notice that when making measurements at a distance that is much larger than the charge separation then  the dipole gives a good approximation of the actual electric field. The dipole is generally represented by a vector which is from the negative charge towards the charge that is positive.

We often notice in subjects like physics the dimensions of a massive object can be ignored and can be treated as a pointlike object that is of a point particle. 

FAQ (Frequently Asked Questions)

Q1. Explain What is the Torque on the Dipole?

Ans: The derivation of the phenomenon torque on an Electric Dipole.

The direction which is of the moment of dipole is from the positive to the negative charge; it can be seen from the above equation that the torque is said to be the cross product of the dipole moment and electric field as well.

Q2. Explain How Torque Affects the Dipole Which is in an Electric Field?

Ans: The electric charges and the Fields. The torque generally tends to align the dipole in the direction of the electric field. That is repulsive in nature since both charges are alike that is positive.

Q3. Explain What is the Torque on a Dipole in a Field Maximum?

Ans: When there is a moment of the electric dipole it is kept in an electric field the force generally acts on both charges in a dipole. The force that is acting on the charges acts as a couple and the torque dipole experiences as well. The torque is said to be the maximum when it makes 90 degrees with the electric field which is the most unstable position.