The energy required to free the valence electrons is called the band gap energy because it is sufficient to move an electron from the valence band or outer electron shell, into the conduction band where upon the electron may move through the material and influence neighboring atoms. The above following diagram illustrates this concept.
Insulators are materials where the electrons are not able to freely move. Examples of good insulators are: rubber, glass, wood,. A battery converts chemical energy into electrical energy by a chemical reaction. Usually the chemicals are kept inside the battery. It is used in a circuit to power other components. A battery produces direct current DC electricity electricity that flows in one direction, and does not switch back and forth as is with AC alternating current.
For more information on Batteries see: How does a Battery Work? A generator usually means a machine that makes electrical energy. It has a generator head with wires, spinning inside a magnetic field. The resulting electromagnetic induction makes electricity flow through the wires. Hybrid electric vehicles carry a generator powerful enough to make them go. When the electrons in the conductor pass through a magnetic field if the field is strong enough and the conductors relative velocity through the field is fast enough then the bonds to their nuclei will be broken and a flow will be induced.
In order to induce a high level of electron flow a great deal of energy is needed in order to create relative velocity between the conductor and magnets. Chemical reactions inside of batteries also create an electromotive force causing electrons to flow in a circuit.
Photons light energy can also cause electrons to flow when they strike a photovoltaic cell. To learn more about how electrons form matter with protons and neutrons please see our page on atoms.
For deeper physics on the electron please see hyperphysics. For more about how electrons are relevant to chemistry please see UC Davis's wiki.
To just play around with different models of electrons around an atom, please see PhET's models of the hydrogen atom. These electrons have rather large velocities, due to the fact that they fill up energy levels just as the electrons in atoms fill up available energy levels. When an electric field is applied, they are mobile and quickly move average net motion, on top of their random motion to cancel out the field, and so a good low-frequency approximation is that electric fields are always zero inside of conductors.
As you say, when a conductor carries a current, the electrons have a net drift velocity which is often quite small. The actual drift velocity depends a lot on the geometry of the conductor, the amount of current flowing, and the density of mobile charge carriers the drift velocity is proportional to the current, and inversely proportional to the cross-sectional area and the density of mobile charge carriers.
But what happens is that a large number of electrons all collectively shift their positions together. When you apply an electric field to a conductor, each electron only has to move a little bit, but all of them move together, and so the net current can be quite high.
Signals propagate along wires at very high speeds. If a wire is perfectly conducting, then the speed of a signal propagating along depends on the insulating material around the wire.
An electric cell often called a battery can supply this energy and make free electrons move in a metal conductor connected between its two terminals.
Electrons flow from the negative terminal through the conductor to the positive terminal. They are repelled by the negative terminal and attracted by the positive terminal. The direction of conventional current. Electric current was discovered before physicists knew about free electrons.
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