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Current vs. voltage

  1. May 19, 2008 #1
    What is the difference between 60Hz voltage and 60Hz current. I know that 60Hz current i believe that 60Hz current is the pulsations of the current. But can someone clear up 60Hz voltage.
     
  2. jcsd
  3. May 19, 2008 #2

    NoTime

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    You will always have voltage as long as the power source is energized.
    You will only have current if there is a load.
     
  4. May 19, 2008 #3
    Actually, in the ac domain, 60 Hz or whatever frequency, the current and voltage cannot exist independently. That is, if one is zero, so is the other. A non-zero voltage can only occur if the current is also non-zero.

    Under time-varying conditions, i.e. "ac", you can't have either one without the other. Maxwell's equations affirm this. When the circuit is "open" or "unloaded", there is a displacement current. When the circuit is shorted and driven with a constant current source, there is a voltage, as a perfect short still possesses inductive reactance.

    At 60 Hz, or any ac frequency, the current and the voltage are both non-zero, or both zero. One is never there without the other.
     
  5. May 19, 2008 #4

    DaveC426913

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    Do you understand the difference between voltage and current?

    Voltage is the potential energy, current is the flow of energy.

    A high current, low voltage source such as your car battery (15A, 12V) could kill you.
    While a low current, high voltage source such as a static shock (~0A, 30,000V) is pretty harmless.
     
  6. May 19, 2008 #5

    rbj

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    only if the power source is a "voltage source" and "a load" is some non-infinite impedance.

    you can also have a current source and in that context, "no load" is a short circuit. then you can say that you will always have current as long as the power source is energized, and you will only have voltage if there is a load.
     
  7. May 19, 2008 #6
    yes i do know the difference between voltage and current. But I was asked by someone with reference to an electronic circuit, if it was to handle 60Hz current or 60Hz voltage. and that kinda stummbled me. Because i know that 60Hz refers to current because of the time varing conditions. 60Hz voltage, well i just don't know what the refers to.
     
  8. May 19, 2008 #7

    russ_watters

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    The way you worded things, I'm not sure you do understand voltage and current. "60Hz" refers to the oscillation frequency of the voltage source, typically a rotating generator. The voltage (which is the electrical equivalent to pressure) varies in a sinusoidal pattern, with a frequency of 60Hz. The resulting current in a circuit (like a mass flow rate) is a function of that voltage and the resistance of the circuit. It will vary in a similar pattern, though capacitance or inductance in the circuit can vary the current waveform.
     
    Last edited: May 19, 2008
  9. May 20, 2008 #8

    NoTime

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    Fair enough, but I think Russ addressed what I perceived to be the OPs question much more clearly than I did.
     
  10. May 21, 2008 #9
    Your car battery is not a constant source, it will not produce 15 amps ideally. If you put 12 volts across your body (which is a really high resistance) you will not be hurt. 12 volts dc is not enough potential difference across any two parts of your body to cause much more than micro amps to flow; unless maybe the points were millimeters apart. If the battery continuously supplied 15 amps and was connected across a load of your body it would need an ass-load more voltage potential to kill you (supply 15 amps).







    The basic analogy is the water analogy for understanding current and voltage.
    You have a 55 gallon drum, and a bunghole tapped at the bottom with a hose connected to it and a sprayer on the end of the hose. The height of the water level in the drum is your potential energy, the higher the level the more energy you have due to gravity. This represents voltage potential. there is water in the hose, even though the sprayer handle is off, so the water being there is the potential energy existing, or the voltage. When you open the valve on the end of the sprayer water pours out, now you have flow, which would be your current. So you can see now how you can have voltage but no current (no water flow).
     
  11. Mar 13, 2009 #10
    The basic analogy is the water analogy for understanding current and voltage.
    You have a 55 gallon drum, and a bunghole tapped at the bottom with a hose connected to it and a sprayer on the end of the hose. The height of the water level in the drum is your potential energy, the higher the level the more energy you have due to gravity. This represents voltage potential. there is water in the hose, even though the sprayer handle is off, so the water being there is the potential energy existing, or the voltage. When you open the valve on the end of the sprayer water pours out, now you have flow, which would be your current. So you can see now how you can have voltage but no current (no water flow).[/QUOTE]

    HI I am new and am basically trying to learn more about electricity and physics because I am a musician and really love tube amps. Just wanted to say that this last use of the water analogy really clenched it for me. Took me a while but now i think I get it.

    thanks!
     
  12. Mar 13, 2009 #11

    DaveC426913

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    Yah, I just wonder if there's an analogy out there that doesn't use the words "bunghole" and "clench" in the same breath. :rolleyes: (That's me, ever a constructive comment...)
     
  13. Mar 31, 2009 #12
    You can also limit current using a PWM. In this case, the voltage remains the same, but is switched on and off several thousand times per second. In essence, this could give you 60 hz current, however you would still have 60 hz voltage as well. The important point is that you can control the current without sacrificing voltage or loosing power through resistance. Also, pertaining to the car battery post. If you cause a short across a car battery, and you come into contact with that, you can generate a huge amount of voltage in your body (because of the high resistance) which will definitely kill you.
     
    Last edited: Mar 31, 2009
  14. Mar 31, 2009 #13
    You cannot limit current without changing voltage. It appears that you are in the PWM case, but you are not really.
    -
    You have a HUGE misconception in the car battery case. Don't post crap like this.
     
  15. Apr 1, 2009 #14
    Haha april fools right??

    PWM controls the amount of power a load receives over time. Instead of diverting the energy to a limiting resistor to control the current through the load you are just turning the current on and off, so no power is wasted through the limiting resistor.
     
  16. Apr 1, 2009 #15
    you could always drain the petcock.
     
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