Fundamentals of Electricity

Electricity and the water hose analogy

Volts = Pressure:

The unit of measure for potential is voltage and the unit is the Volt and this is the symbol.

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Voltage, like water pressure, is a relative measurement. Pressure can be measured at any spot along the hose relative to any other spot. Overall pressure is the difference in pressure between the input of the hose and the output.

		o	Voltage, like water pressure, can be present whether there is current flowing or not.
		o	Another way of describing Voltage is potential energy us simple potential.

Amps = Current:

The unit of measure for current is the Ampere (or Amp) and this is the symbol.

•	The actual term is Amperes, but almost nobody uses that term today.

•	The number of drops of water passing by a given cross-section of the water hose per second.

•	Current can be increased by increasing pressure or by reducing the resistance to flow.

		o	Electrical current can only flow in a completed circuit.
		o	In a direct current (DC) circuit, the current always flows in only one direction.
		o	In an alternating Current (AC) circuit, the current alternates so that it flows back and forth.

Ohms = Resistance:

The unit of measure for resistance is the Ohm and the the Greek letter Omega is the symbol.

•	While water current is flowing there will always be a difference in the amount of pressure on each side of a partial constriction.

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With electricity, while current is flowing there will always be a difference in the voltage on each side of a resistance. This difference in electrical potential is an indication of how much energy is being consumed by the resistance.

•	Any constriction in the hose or reduction of the number of parallel hoses, adds resistance to flow.

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There is a good reason why this is the electrical symbol for resistance. You can easily imagine what effect a hose shaped like this would have on the flow of water.

•	In a water hose, if you enlarge the diameter of a section or add multiple parallel hoses, you reduce the resistance to flow exhibited by that section.

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Exactly the same thing happens with electrical current.

Watts = Power:

Power is a function of potential and the amount of current flowing. The unit of measurement for power is the Watt and this is the symbol.

•	In real terms, it is a measurement of the amount of work being done by the flow of water through the hose.

		o	In electrical circuits this is the same thing. Power cannot be read in a circuit without current flow because only potential energy (voltage) is present.
		o	The higher the voltage, the lower the current needs to be to produce a given amount of power.
		o	This is why the high tension power lines run hundreds of thousands of volts. By doing so, they can reduce the amount of current, thus the required diameter of the conductor to deliver the same amount of power. Cables in car stereo systems have to be so thick because with only 12Volts of pressure, it takes more current in Amps to deliver the Wattage the speakers demand.

How they all interact:
Voltage, amps and resistance all interact to determine how energy is used in a circuit.
The Ohm's Law formula is E = I X R

Where E=Electrical Voltage, I=Current in Amps and R=Resistance in Ohms. The graphic illustrates the recursive nature of the equation. If you know any two of the values, the third is a simple calculation E = I X R, I = E/R, R = E/I

Power in Watts has a similar relationship with Voltage and Current.
Here the formula is P = E X I

Where P=Power in Watts, E is again Voltage and I is again Current in Watts.     A handheld hair dryer at 1,500 Watts (1500/120 Volts = 12.5 Amps = thin cable)     1,000 sub-woofer in a teenager’s car stereo (1000/12 Volts = 83.3 Amps = fat cable)