Ohm's Law
     
(E) Volt: Measured in Volts
The practical unit of voltage; the pressure required to force one ampere through a resistance of one ohm. To make electrons flow in a conductor, an electrical pressure must be applied and this is called electromotive force (EMF) or voltage.
     
(I) Current: Measured in Ampere
The practical unit of electric current flow; the electric current that will flow through one ohm under a pressure of one volt.
     

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(R) Resistance: Measured in Ohms
The opposition which a device or material offers to the flow of current; the opposition which results in the production of heat in the material carrying the current. Resistance is measured in ohms. The practical unit of electrical resistance: the resistance through which one volt will force one ampere. All resistances have two dimensions: Cross-sectional area and length.
       
Electrical Power is equal to voltage times the amperage.

W= E x I
       
(W) Power: Measured in Watts
The rate at which electrical energy is delivered and consumed. Power is measured in watts. A motor produces mechanical power measured in horsepower. A heater produces a heat (thermal) power. A light bulb produces both heat and light power ( usually measured in candlepower).
       
Ohm's Law states:
In a DC circuit, the current is directly proportional to the voltage and inversely proportional to the resistance. In other words, the water flowing in a pipe (amperage) will be increased if the water pressure (voltage) is increased. And, if the restriction (resistance) in the pipe is less, the water flow ( amperage) will be more.
 
This is true for all DC circuits. However, AC circuits require an additional factor in the equation. There are two ways to measure AC voltage, Peak-to-Peak (PP) and Root Means Square (RMS). The PP is measured from the highest point of the waveform to the lowest point of the same cycle. But this voltage do not represent the true picture. Most all electrical formulas for AC circuits use the RMS value. To get the RMS value, multiply the PP voltage by the constant 0.707 to get the correct value.
 
Most DVMs (Digital Volt Meters) only measure peak-to-peak Check your DVM to determine if it will measure RMS (or True RMS). Also check your equipment manufactures specification to determine if their number are for PP or RMS.
       
Looking at it in another way.
  • The generator is liked a water pump, the prime mover.
  • The conductor is like the water pipe, the larger the conductor, the less the resistance and the more flow.
  • The voltage is like the water pressure, the force pushing.
  • The amperes are like the flow of water, an amount of current flowing is like the gallons per minute in water.
  • The resistance is like the restriction in the water pipe. A reduction in the water pipe size would cause opposition to the amount of gallons per minute, as would the resistor in an electrical circuit. It limits the flow of the current.
  • Watts ( power) is expressing the rate involved; the power required. With water it requires more work to pump water up to a water tower that it would to pump water at ground level. Wattage is the rate at which the electrical energy is changed into another form of energy, such as light or heat. The faster a lamp changes electrical energy, the brighter it will be.
       

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