Dipolos eléctricos y momento dipolar

When two equal but opposite point charges are held together, the pair is called a dipole. If it does not separate due to external forces, it is called a permanent dipole.

In a water molecule, the centers of negative and positive charges are close but do not coincide, making it a permanent dipole.

In a uniform electric field, the charges experience forces that are equal but opposite, resulting in zero net force. However, the dipole experiences a net torque.

Choose any origin, and consider the position vectors of the charges. The torque on each component is obtained.

Upon vector addition, the net torque is given by the cross product of a new vector with the electric field. It is the product of the charges' magnitude and the displacement vector of the positive charge with respect to the negative charge. This is called the electric dipole moment.

The torque rotates the dipole along the field.

If it is anti-parallel, it experiences zero net torque but is in an unstable equilibrium, as slight deviations lead to a torque that rotates it parallel.