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Some basic definitions, equations and analogies of electricity.
|Symbol||Unit||Description||Water Analog||Elec. Units||Base Units|
|Voltage||V||volt (V)||Pressure (Potential) difference due to charge difference||Head: Pressure (Potential) difference due to height difference||J/C||kg•m²/(s³•A)|
|Current||I||amp (A)||Flow of charge in charge/time or coulombs/sec||Flow: Flow of water in volume per time such as liters/sec||C/s or W/V||A|
|Resistance||R||ohm (Ω)||Opposition to the flow of charge||Friction: Opposition to the flow of water||V/A||kg•m²/(s³•A²)|
|Power||P||watt (W)||Energy/Time also Power=Current (I) * Voltage (V)||Power: Power=Flow (Q) * Pressure (H)||J/s or A•V||kg•m²/s³|
|Energy||E||watt-hour (Wh)||The ability to do work||Energy: The ability to do work||3600 J||kg•m²/s²|
- look familiar, see P=Q*H*e/k from microhydro power
- I=V/R might be more edifying since current is usually the result of pressure acting on resistance.
- This only applies to ohmic circuits, those circuits which display a linear relationship between current and voltage (i.e. the resistance does not change based upon current or voltage).
|VT=V1+V2+…||V stays same|
|I stays same||IT=I1+I2+…|
The following animated analogy illustrates the operation of direct current (DC) circuits.
|Water Tank - Electricity Analogy|
|Tank Vertical Difference||Battery Voltage Difference|
|Water Flow||Electrical Current|
|Mechanical Energy Appliance (Blender)||Electrical Energy Appliance|
For each example, ask yourself:
- How fast will the battery run out?
- How fast will the virgin margaritas be made?
- And most importantly why?
If you would like to do math to support these analogies, use:
- Feet = volts
- GPM = amps
- Each blender has a resistance of 6 Feet/GPM = 6 ohms
1 Tank 1 Blender
- This is the test case (datum).
1 Tank 2 Series Blenders
- The flow is 1/2 the speed of our test case.
- The two blenders in series are each going 1/4th the speed of our test case.
1 Tank 2 Parallel Blenders
- Each blender is at the same speed as our test case.
- The flow from the tank is twice as fast as our test case.
2 Parallel Tanks 1 Blender
- The blender is the same speed as our test case.
- The flow from each tank is half as fast as our test case.
2 Series Tanks 1 Blender
- The blender is 4 times the speed as our test case.
- The total flow is twice the speed as our test case.
PS The second tank has a lid that keeps it closed.
See Rural Electrification Systems for more background information (these page should be integrated together).
- Everything you every wanted to know about Lead Acid batteries.
- Car and Deep Cycle Battery FAQ
- Fantastic site on physics in general. Easy to understand, but accurate information on DC Circuits.
- HyperPhysics - DC Circuits
- Some easy to follow basic theory.
- Lesson 3: Electricity - Colegio Franklin Delano Roosevelt
- Some more information on electricity. Not wrot with error like at least one of their other pages.
- How Stuff Works - Electricity
- Understanding current