Dipole and Quadrapole Moments

Just imagine that there is a body, which is electrically neutral. The body must be very much separated in terms of charges and as a result, the maximum quantity of positive charges should be at one end and the maximum number of negative charges should be at the other end. These types of bodies are nothing but electric dipoles. However, the major condition here is that the body should be absolutely electrically neutral. This means that the body, when it is placed in a uniform electric field will never experience any kind of outward force until it experience some magnitude of torque. The torque’s magnitude will be highly dependant on the orientation with regard to the field. The magnitude of torque is found to be maximum, at the two ends of the body, where the concentration of either positive or negative charges is more.

The dipole moment can be defined as the maximum magnitude of torque experienced by the electric dipole when placed in an electric field. The dipole moment is a vector quantity since it is dealt in terms of both magnitude as well as direction. In order to experience the maximum magnitude of torque, the dipole moment should happen at the right angles with respect to the electric field. The relation between the torque, electric field and dipole moment is given by the equation τ = p × E, where τ symbolizes the torque, p symbolizes the dipole moment and E symbolizes the electric field.

Speaking about the quadrapole moments, consider that there is a system full of charges, which will not have net charge or net dipole moment. If the system has a set of two dipoles, then it is called quadrapole and the moment occurring here is called Quadrapole moments. Unlike dipole force, it will never experience a net torque or net force.

Questions:

• What is dipole moment?
• What is quadrapole moment?