When opposite electric charges are brought close to each other, they exert an attractive force on each other and move towards each other. This behavior is dictated by Coulomb's law, which states that the force of attraction between two opposite charges is directly proportional to the product of their magnitudes and inversely proportional to the square of the distance between them. Here's the mathematical formulation of Coulomb's law:

F = k * (q1 * q2) / r^2

Where:

- F is the electric force between the charges (measured in Newtons, N)

- k is the electrostatic constant approximately equal to 8.988 × 10^9 N⋅m^2/C^2 in SI units (N m²/C²)

- q1 and q2 are the magnitudes of the electric charges (measured in Coulombs, C)

- r is the distance between the charges (measured in meters, m)

If we take two equal negative and positive charges, let's say electrons and protons, and bring them close to each other, the positive charge (protons) will exert an attractive force on the negative charge (electrons), causing them to move towards each other until they are at an equilibrium distance.

This attractive behavior of opposite charges forms the basis of many fundamental principles in electricity and magnetism, such as the attraction between charged particles in an atom, the formation of electric circuits, and the functioning of electrical and electronic devices.