What four things are needed to complete an electrical circuit?

Every electric circuit, regardless of where it is or how large or small it is, has four basic parts: an energy source (AC or DC), a conductor (wire), an electrical load (device), and at least one controller (switch). Visualize what happens when you switch on a room light.

IMPORTANT:  Frequent question: What is the direction of the electric field caused by an infinite line charge arranged along the z axis?