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Confused about voltage & current -- Please check my understanding

  1. Feb 19, 2017 #1
    • Member advised to use the homework template for posts in the homework sections of PF.
    Hello, This is not a homework but I’m confused about current and voltage. My understanding is fragile and I need to reinforce it with your help. Below I’ve written what I think I know to be correct. Please correct me where required. This is high school physics.


    (i) Current is the rate of flow of electrical charge. Charge is measured in coulombs.


    (ii) One coulomb of charge is a collection of 6·2 x 1018 electrons. So current is the rate of flow of coulombs.


    (iii) The number of coulombs flowing per second is the current. Current is measure in amperes.

    (iv) Voltage is the number of joules of energy the coulomb has (collection of 6·2 x 1018 electrons) OR the number of joules of energy the coulomb has is the voltage. [I had to say this both ways because I need to reinforce it in my brain].


    (v) Voltage (joules of energy per coulomb) (or push) is given to the coulombs (collection of 6·2 x 1018 electrons) by the battery or power-station.



    (vi) To use an analogy of a river here: If the battery is on a steep incline it can provide lots of voltage (joules of energy per coulomb) (or push due to gravity) to the coulombs (cups of water). The number of coulombs (cups of water) per second flowing down the hill is the current of the river.


    (vii) You cannot have current without voltage BUT you can have voltage without current because voltage is the just the potential to deliver joules of energy per coulomb (voltage)???


    (viii) Delivery of the voltage (joules of energy per coulomb) only happens when the circuit is complete and the electrons are flowing (current).


    (ix) If a wire has a voltage or potential difference of 100V. This means that the wire is connected to a battery, that has the potential to give 100 V of voltage (joules of energy per coulomb) (or push) to the electrons in the wire??? BUT this only happens when the circuit is complete (+ve terminal is connected to the –ve terminal of the wire).


    (x) If a battery in a circuit has potential to supply of 100 V, is connected to a wire of low resistance then the current will be high because V/R = I. The high current will make the wire hot. A low current would result in less energy loss through heat.


    (xi) When we talk of the potential difference across a wire, this is the same a voltage across the wire. This will depend on the power supply to which the wire is connected. The voltmeter is measuring the joules of energy per coulomb (volt) between two points.


    Thank you for your help.
     
  2. jcsd
  3. Feb 20, 2017 #2

    andrevdh

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  4. Feb 23, 2017 #3
    Seems about right! :)

    I don't know what you're wanting to do (are you an engineer, is this a hobby, etc.?) but another good resource is the Feynman lectures Vol II - http://www.feynmanlectures.caltech.edu/II_01.html

    You can't really dip in and out of them - it's probably best to make time to sit down and read a chapter (there are quite a lot of diversions and side routes.) But in terms of making tangible analogies to the concepts, they're excellent.
     
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