- Volts & Amps -

Voltage and current are two very fundamental definitions used in the study of circuits. Understanding the connection between voltage and current is the basis for understanding electricity.

Current is the flow of electrical charge, the amount of charge that passes a point each second. Charge is measured in Coulombs, so current (the rate of flow of charge) is measured in Coulombs/second. A Coulomb/second has been given the name Ampere (a), usually called an amp. One Coulomb has a lot of charges, about 16,000,000,000,000,000,000. The charge on electrons is negative. Sixteen billion billion electrons make a charge of -1 Coulomb.

Voltage is the amount of energy each Coulomb of charge. The unit for energy is the Joule, so voltage is measured in Joules/Coulomb. A Joules/Coulomb has the name Volt (V). Voltage is often visualized as the "push" behind current.

An Analogy:
To help visualize the meaning of volatage and current, you can make an analogy to a platoon of soldiers completing a 10 mile hike in formation. The soldiers could represent individual charges, the flow of marching solders (number passing each second) could represent the current, and the energy each soldier has could represent the voltage. In a simple series circuit, where the soldiers have only one path, the current will be the same, because no soldiers are gained or lost on the hike (hopefully!). The voltage will decrease as the charge flows through the circuit like the solders tire during the hike. As the soldiers march through swamps and tire there will be less energy per soldier. In an electrical circuit charges lose energy passing through resistors or other components that uses power. For a successful march, the soldiers must have energy enough to return to base. No soldiers are lost. In an electronic circuit the charges always have enough energy to return to the battery. No charge is used up.

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