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What governing factors determine how loads are powered?

  1. Aug 23, 2012 #1
    Hi,

    I was wondering, what are the governing factors that control how loads are powered by circuits? If a 300hp motor is connected to Source A, Source A will supply 300hp of power at whatever the specified voltage is. But at the atomic/subatomic level, what really determines how that power is "shipped" to the motor?
     
  2. jcsd
  3. Aug 23, 2012 #2
    It isn't power that is being shipped it is the forced motion of electrons being manipulated to do something useful.

    The governing factors are: voltage(V), current(I) and resistance(R).

    Source A has a voltage potential. Once connected to said motor, which has a certain amount of resistance it will permit a certain amount of current to flow through. Specifically V/R = I ( ohms law ). It's the current ( flow of electrons) as a result of potential difference on a conductive wire that allows that "power to be shipped". I hope i understood your question correctly
     
  4. Aug 23, 2012 #3
    Yes, I'm aware of Ohm's Law. I understand that at the endpoint (or, the load) the energy held in the charged electrons will mostly be converted to do useful work, while some will be converted into photons which are felt as heat.

    I think I may be struggling to determine what it is that I want to ask, but I feel that it's the starting point that gets me confused. Why does a power source -- be it a battery, a solar panel, or a generator -- decide to output 300hp of power to a 300hp motor? Why not deliver 250hp to a 300hp motor? Yes, Ohm's Law does play a role in this, but there must be a deeper answer than simply that. How does the source see the load and know exactly what amount of energy is needed to perform the task required of the load?
     
  5. Aug 23, 2012 #4
    I don't know what power source you're referring to that can do such a thing. A battery for instance does not determine anything, it provides a potential difference. Lets say for instance we have a 300 hp motor with a resistance of R, just because i hook it up to an electric power source doesn't mean it will dissipate 300 hp. Horse power is related to wattage by 1 hp = 746 watts. Electric power in wattage is calculated by voltage*current. So if i wanted to know what potential to run across this motor to achieve its 300 hp rating :

    746*300 gives us its power consumption of 223800 watts
    223800/R = would tell us the voltage required run the motor with 300 hp.

    I think you're using the terms energy and power a little too loosely. In physics and electrical engineering they are related but are not one and the same.
     
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