Electromagnetics

It gives the electrostatic force between two point charges: F = (1/4πε₀)·(q₁q₂/r²). The force is inversely proportional to the square of the separation distance and acts along the line joining the charges.

The electric field is the force per unit positive charge: E = F/q, with units of volts per meter (V/m) or newtons per coulomb (N/C). E points in the direction a positive test charge would be pushed.

E = (1/4πε₀)·(q/r²), directed radially outward for a positive charge and inward for a negative charge. The field magnitude falls off as 1/r².

∮ E·dA = Q_enclosed/ε₀. The net electric flux through any closed surface equals the total enclosed charge divided by the permittivity of free space. It relates field flux to enclosed charge, independent of charge distribution outside.

Electric potential is the work per unit charge to move a charge from a reference to a point: V = W/q, measured in volts. The field is the negative gradient of potential: E = -∇V; equivalently V = -∫E·dl.