open&close circuit and conductor

Electrons always have a negative ("-") electric charge, and it is this electric charge that is responsible for what we call electricity. When electrons move from one place to another they take that negative charge with them. It is this movement of charge that we refer to as electricity!
This movement or flow of electrons is called an electric current. We often find electrical currents inside wires that conduct electricity. Conductors are materials that contain many freely moving electrical charges (like copper, silver, aluminum, and gold). Insulators are materials that contain few moveable electric charges (like plastic, glass, rubber, and air).

An electrical current traveling through a wire. Electrons don't really race from one end of the wire to the other like sprinters at a track meet. In an electric current the electrons jump from one atom to another, pushing other electrons in front of them as they go. They really behave more like runners in a relay race, passing along the baton (electrical energy) from one atom to the next. The electrons don't actually travel very fast, but the electrical energy that they create travels at the speed of light!

Electrons move along a path called a circuit if a "pushing" force (a source of electricity) is part of the circuit. Sources include things like batteries, wall outlets, and solar panels.
While the electrons are moving through the conductors, the circuit is complete, or "closed." If any part of the circuit is removed, the electrons stop and the circuit is "open." You've probably opened and closed circuits before without ever realizing it: When you turn the lights on or off, you are closing or opening a circuit!

reference : The NASA Sci Files, Dr. D's Lab

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