A circuit that is wired completely in series is just a single loop, which means that there is only one path through which current can flow. The current across each element is therefore the same because it never gets split across two different paths. In this circuit diagram, two resistors are wired in series:
An electric circuit is simply a connection of electrical elements. A light bulb connected to a battery is a basic circuit. The battery delivers voltage to the system, and the light bulb introduces resistance.
The standard unit for measuring electrical power is the Watt, which is equal to 1 Joule/second. In the context of electricity, power is often used to describe either an electrical device or a generation system. In the first case, the power rating of a device gives its instantaneous electrical demand. For instance, in order to remain lit, a 10-Watt compact fluorescent light bulb would continuously require 10 Watts of electrical power.