How to Find the Force of a Dipole?

Two electrical charges, ‘+Q’ and ‘-Q’, when separated by a distance ‘d’ between them, form an electric dipole where the mid-point of +Q and -Q is known as the centre of the dipole. By default, the direction of an electric dipole is taken from the negative charge -Q to the positive charge ‘Q’. The electric field lines are drawn from the positive to the negative charge. The total charge of an electric dipole is zero as (+Q) + (-Q) = 0.  What is the formula for an electric dipole? Please read the article to find out the dipole moment, its significance, the electric dipole formula, the electric field of a dipole, and the force on the electric dipole.

Dipole Moment

An electric dipole moment is the product of one of the charges and the length between them and is a vector quantity. A dipole moment develops when two charges, equal and opposite, are brought in the close vicinity of one another and are either attracted or repelled due to the force between them. What is the dipole moment formula? It will be answered subsequently. A dipole moment exists between charged quantities such as molecules (HCl, H₂O, etc.). Such molecules have a fixed dipole moment since their charges do not coincide; the dipole moment being a vector quantity, it has a specific magnitude as well as direction. Such molecules are called polar molecules and are also significant to study the concept of polarisation.

Dipole Significance 

• The concept of dipole holds a physical significance as it is a vector quantity that gives the measure of polarisation or polarity for a system; a dipole comprises two equal and opposite charged particles separated by some distance. 
• What is the formula for an electric dipole? It comprises the charge multiplied by the distance between them. The SI unit of an electric dipole moment is measured in Ampere-metre (Am). 
• The net charge is zero for a dipole of two opposite charges, unlike the dipole moment or the electric field. However, a dipole moment has a magnitude as well as a direction, so it measures the tendency of a dipole to align into the direction of an externally applied electric field, either parallel, anti-parallel or perpendicular to the electric field.  
• The dipole enables us to distinguish between the ortho, meta, and para isomers, cis and trans isomers and tells us that symmetrical molecules have a zero dipole moment. 

Electric Dipole Formula  

Suppose two charges, ‘Q’ and ‘-Q’, are separated by distance d between them such that d=2a, which is the distance from the middle of the dipole to each charge. The electric dipole moment ‘p’ will be,

p = Q x d 

also, 

p = 2a

Electric Field Of A Dipole  

The electric field is defined as the influence that can be felt by a charged particle; hence, for a dipole containing two charged particles, an electric field is associated with it. The concept of an electric field of a dipole is important to understand dielectric and polarisation. To calculate the electric field, consider a dipole having charges ‘Q’ and ‘-Q’ separated by a distance d. The direction of a dipole is from negative to positive, while the direction of the electric field is from positive to negative. By a series of mathematical calculations, the electric field for a dipole along a perpendicular bisector is E= -Kp/r³, and the electric field along the axis of a dipole is E = 2Kp/r³.

Force on Electric Dipole  

What is the force on a dipole? A dipole in the uniform electric field has a net charge of zero, which implies that according to the formula F=QE, where F is the force, Q is the charge, and E is the electric field, the force would be equal, and in the opposite direction for a dipole. Hence, net force F = (QE) + (-QE) = 0. This means that for a dipole in a constant electric field, the net force is zero on the system. 

• However, in the case of a non-uniform electric field, the dipole will experience a net torque because the force on the charges of the dipole forms a couple, and, in that case, the net force will not be zero. 

Conclusion 

A dipole consists of opposite charges separated by a distance between them; dipole moment is a vector quantity measured in Ampere-metre. A dipole holds physical significance while studying the polar molecules and electrical charges as it has a fixed value for the molecules whose charges do not coincide. The direction for a dipole is taken from negative to positive by convention; by a series of mathematical calculations, one can calculate the electric field and force for a dipole as described in the text. It also answers the question, What is the formula of electric dipole?