Putting Charge in Motion - Voltage, Current, and Circuits

Thus far, we have only discussed "static" (stationary) charges.  Static charges alone are useful, but not nearly as much as charges in motion.  As you recall, electrons are the most easily moved particles. 

 Recall the Galvani experiments discussed in class:
So, electrons are moved by the chemistry of the electrochemical/voltaic cell (originally called the "electric pile" and now simply, battery).  Here are pictures/diagrams of Volta's original batteries:




There is a chemical reaction between the electrolyte paste (often an acid) and the two metals (often zinc and carbon).  Electrons are given up by one metal (zinc) and accepted by another (carbon or copper).  The motion of electrons is called "current", but we usually imagine that it is positive charge moving (to keep the numbers positive).

We can't see electrons, but we can certainly see what they do when they pass through a filament in a light bulb:



We need to define new quantities in electricity:  voltage, resistance, power.



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