This document discusses electric circuits and current. It explains that circuits are either open or closed, with closed circuits allowing electricity to flow continuously through a complete loop that includes a power source, conductor, and load. Closed circuits have electricity flowing from the positive end of a battery through a wire to a light bulb and back through another wire to the negative end of the battery. Conductors like copper wires are used to carry electric current because they allow electricity to flow through them. Switches can be installed in circuits to open or close the circuit as needed.