 Here's a couple of examples of how this electromagnetic force works. When two electrons approach each other, their charge generates a disturbance in the electromagnetic field. This disturbance pushes them apart and their paths are bent outward. The same is true if an electron and a positron pass near each other. The disturbance in this case is similar in type but different in its details with the result that the oppositely charged electron and positron are attracted to each other. Their paths are bent inward. Here's the Feynman diagram for an electron-electron interaction where the photon field mediates the force that changes the momentum of the two electrons. One says they exchange virtual photons but this is just jargon. The diagram is used for convenience. A virtual particle is not really a particle at all. A particle is a nice regular ripple in a field one that can travel smoothly and effortlessly through space. This virtual particle is a disturbance in the field that will never be found on its own. It doesn't have the energy to become a well-formed ripple moving through space. This kind of disturbance will decay or break apart once its cause is gone. This kind of interaction between the electromagnetic field and the electron field is important because the force that the two charged particles exert on each other is generated by this interaction. This force is one of the four fundamental forces in nature. They are characterized by a coupling constant. The coupling constant for the electromagnetic force is 1 over 137. We will use the electromagnetic force as a model for the strong and weak nuclear forces. The complete picture of what is going on with electromagnetism is still an area of active research called quantum electrodynamics, or QED for short.