Trying to get intuitive understanding of voltage/current/resistance

Discussion in 'General Electronics Chat' started by coolpontiac, May 17, 2014.

  1. coolpontiac

    Thread Starter New Member

    May 17, 2014
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    Welcome to AAC!

    A thread belongs to the OP (original poster). Trying to take over someone elses thread is called hijacking, which is not allowed at All About Circuits. I have therefore given you a thread of your very own.

    In addition, you have practiced the arcane art of necromancy, the revival of a long dead thread. Likely the OP (Original Poster) has solved his problem in the years that has passed, or thrown it away, or something.

    This was split from Trying to get intuitive understanding of voltage/current/resistance

    since power is conserved , why can you deliver more power (VxA) in a given size wire by using higher voltage.

    my Q is really about why you seem to get a 'free ride' with higher voltage. arent you really pushing power thru a wire?

    e.g. a 1 hp motor that runs on 1000v vs 10v, you can use a much smaller wire but you are 'making' the same effort. where am i going wrong ?
     
    Last edited by a moderator: May 17, 2014
  2. crutschow

    Expert

    Mar 14, 2008
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    Yes power is being delivered the wire but it's not a separate entity. It's a result of the volts times the amps as you noted. Since power is V x A and the resistive power loss in a wire is proportional to the Amps then if you increase the Volts, you can have more power delivered to the load by the same Amps with no additional resistive power loss in the wire.

    Using the water analogy, the water power delivered at the end the pipe (say to a water turbine) is proportional to water flow rate (amps) and the water pressure (volts). So the higher the pressure the more power delivered for a given water flow.
     
  3. studiot

    AAC Fanatic!

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    Power is not a conserved quantity in physics.

    That distinction is reserved for Energy, as in the law of conservation of energy or the First Law of Thermodynamics.
     
  4. nsaspook

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    Yes, you're making the same effort but the mix of how the power is delivered is different. Current is defined as the movement of charge in the wire. (electrons) In a normal conductor those electrons require a slight amount of energy (seen as resistance with a voltage across it) to move from their normal rest position in a section of the wire. The better the conductor the easier it is for them to move for a given cross section of wire. You can make the wire bigger so more can move from the same amount of force (voltage) allowing more current without energy being wasted as heat from resistance as a voltage drop. The other way to avoid the voltage drop is to increase the voltage so less charge (current) needs to move at a given power level reducing the effect of the wire resistance and the percentage of voltage drop to the voltage supply.

    Because the power in the circuit is carried by the electric and magnetic fields around the wire instead of the electrons in the wire, reducing the amount of electrons (and the wasted power needed to move them) needed to produce those fields increases power transfer efficiency when resistance in conductors is significant until you run into things like insulation requirements and safety.
     
  5. studiot

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    Power is the product of voltage and current.

    The voltage is determined by the power source.

    for example the 230 volts from a wall socket or 9 volts from a battery.

    Once you have your source, the voltage is fixed.

    The current is determined by the load. Connect a different load to the source and the current will be different.

    for example a 1000 watt electric fire or a 0.100 watt radio.

    Neither the current, nor the voltage, nor the power is determined by the wiring.
    The wiring can be long or short, fat or thin or even non existent (you can touch your load to the terminals directly)

    and this makes no difference to the voltage, current or power

    Note I have said that you can vary the load on a given source, but I have not said you can vary the source for a given load. That converse is not normally true.
     
  6. nsaspook

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    I assume you mean this if conductors are perfect. (0 resistance)
    Obviously real world wiring is important to loads at a given current level and voltage otherwise we could wire a house with 24 gauge wire.
     
  7. studiot

    AAC Fanatic!

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    Coolpontiac is clearly a beginner so we must reply in suitable basic terms, before he can progress to electrician first class.

    I knew some wag would start arguing, but the niceties only make it difficult for a beginner.

    BTW don't the NSA shell out for you to wire your house with superconductors?
    :D
     
  8. nsaspook

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    I think it's important not to have a completely electron centric view of electricity from the beginning. It's important to understand the close relationship between fields and charge early as a concept (without the mathematical baggage as this forum does) so when you get to the dirty details in circuit theory later it's not a new idea.
    ...

    I gave up my clearance long ago so more more toys unless I sign another contract with the devil.
     
  9. studiot

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    I agree this is essentially an engineering forum with pure science an addendum in the corner.

    Surely your handle should read nsaspook(retired) then?

    Oh I forgot, you guys only retire to Arlington.

    :D
     
  10. ErnieM

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    These guys take their secrets to the grave with them.

    There is no retirement.
     
  11. nsaspook

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    The only thing my long ago past service does is slow instant government background checks (like on guns in the US) because you have a locked record on file somewhere so some clerk has to check it manually. :(
     
  12. studiot

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    guvermint checks m'boy??

    I don't get out of bed for less than $1,000,000

    :D
     
  13. nsaspook

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    I wish. Lets just say I had some youthful indiscretions in the acquisition of technology what were set aside in exchange for my soul.
     
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