How can the total amount of mobile charge in a capacitor
be the same after
charging as before charging?
All capacitors have two kinds of charges: protons (positive charges),
electrons (negative charges). An UNCHARGED capacitor has equal numbers of
protons and electrons on each side. Each side has a charge of zero. Each
side is balanced.
When you charge a capacitor, you move some electrons from one side to the
other (through the circuit, often a battery). The protons stay put. Now
one side has a POSITIVE charge and one side has a NEGATIVE charge. The
TOTAL charge for the whole apparatus is still zero. The total number
electrons and protons are the same. When you charge a capacitor, you do not
add or remove charge: you rearrange the charges.
Dr. Ken Mellendorf
Illinois Central College
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Update: June 2012