"A coulomb is the amount of charge that passes a point through a wire carrying one Ampere for one second. Voltage is a measure of electrical potential energy in units of volts or joules per coulomb (energy/charge). Then 1 volt means 1 joule per coulomb; 2 volts mean 2 joules per coulomb, and 5 volts mean 5 joules per coulomb." Discussion
"It does seem like a strange combination of units, doesn't it? A coulomb is a quantity of electrical charge. As an analogy, I'm going to use a gallon (or litre if you're an SI person) as a quantity of water. I can lift the water and give it gravitational potential energy. The higher I lift, the more gravitational potential energy it has. Thus, the joules per gallon (energy per unit volume) varies depending on how high I lift the water. The same goes for voltage, which is joules per coulomb (energy per unit charge): the higher I "lift" the charge (i.e., the higher the voltage), the more potential energy it has." Discussion
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