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  Electricity - Voltage and Current Teacher's Notes  
  Voltage
Everyone uses this term, even though they might not understand it. You probably know that a single cell from a flashlight creates an electrical force of 1.5 Volts. You also know that a transistor radio battery (with the snaps on the top) creates an electrical force of 9 Volts. (There are six little cells of 1.5 Volts each inside of the 9 Volt battery.) You know that household electrical outlets are 110 or 120 Volts, and you know that "High Voltage" is dangerous.
 
What else should you know about voltage? Again, lets look at the atomic level.
 
Every atom has its own complement of electrons. In a conductor, some of those electrons can jump from atom to atom. But electrons don't move from atom to atom without a reason. When electrons are flowing there is always an electrical force pushing them along. We refer to this force as "Voltage".

 
 
  Current
Again, everyone uses this term without really knowing what it means. In very simple terms, current is the flow rate of the electrons in the circuit. How is that different from voltage? Let's use a water tank and a pipe as an example.
 
In some neighborhoods you'll see a water tank raised high above the ground on strong legs. The water in this tank has been raised up there to create pressure in the system. A series of pipes carry the water down from the tank, under ground, into your house, and then to each sink, bathtub, and toilet. The water in your pipes is under pressure because the water in the tank is pushing down on it. This pressure is similar to Voltage. Voltage is the pressure pushing on the electrons in a circuit.
 
If all of the faucets in your house are closed, no water flows through the pipes. If you open one faucet, some water flows. If you open all of the faucets, a lot of water flows. This flow of water is similar to electrical Current. Current is the flow rate of electrons through the circuit.
 
 
  Are Voltage and Current Related?
Voltage and current are not the same thing, although they are closely related. In simple terms, Voltage causes Current. Given a Voltage and a path for the electrons, current will flow. Given the path, but no Voltage, or Voltage without the path, there will be no current.
 
 
  A Simple Circuit
 
flashlight

 
This picture illustrates a single cell pocket flashlight. The 1.5 Volt cell is pushing the electrons through the bulb and the wire. Without this push, the electrons would be happy to remain stationary. In this case, chemical action within the battery causes the push. When the battery gets old, its chemical reaction slows down and its internal push gets weaker and weaker. (That's why the bulb gets dim.)
 
 
  Who Does the Work?
Current, not Voltage, does the work in electrical circuits. The flow of water through a turbine is what makes the turbine spin. The flow of current through an electrical circuit is what lights the bulb, heats the stove, runs the motor, etc. Routing and controlling the flow of current is the goal of every electrical circuit.
 
 

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