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Electric circuit, current flowing due to battery

  1. Sep 15, 2014 #1
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    1) I don't understand why current flows, for example when you have a source, it has 2 poles, + and -: then the electron should go towards +, if it's in the position 'D', it should just be stuck -- my theory is that because the electron that's in 'A' "enters the battery", so the battery has excess of electrons (because of ion travel and all that), and it pushes that electron in 'D', which again pushes the first electron mentioned... OR the small el. potential on + side of the battery only works in one direction, that is, it attracts the electrons in 'D' area THROUGH the wire around (A, B, C ... D)?

    2) In my book it says that when you connect two amp-meters in a circuit e.g. before and after a resistance (a light bulb), both will show the same current intensity, [itex]I_1=I_2[/itex]. I cannot understand this. Is it actually because the real resistance is caused by electrons themselves because electrons repel each other, and if the first electron (that's in the resistor) slows down, the one behind him does too? Then the whole circuit 'slows down', because when electron finally exits the resistor it wants to reach + but cannot because of the electrons in front of him (that are slow because...)?
     
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  3. Sep 15, 2014 #2

    davenn

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    hi there

    for 1) ... battery basics ... a chemical reaction in the battery moves ions towards the positive terminal and electrons towards the negative terminal.
    When an external circuit is formed between the negative and positive terminals electrons flow from the negative to the positive via that circuit. At the positive terminal, the electrons and ions recombine.

    That separation of electrons and ions in the battery is what produces the potential difference between the terminals

    2) Yes, in a series circuit, the current flowing is same where-ever it is measured, so the meters A1 and A2 will read the same.
    Keep in mind that the speed of the electrons through a circuit is VERY slow google electron drift for an explanation.
    A resistor is not as good a conductor as the wire, it has less free electrons. This has the effect of limiting the number of electrons flowing through it. As the electrons flow through the resistor they also loose energy as heat.

    Does that help ? :smile:

    Dave
     
    Last edited: Sep 15, 2014
  4. Sep 16, 2014 #3
    Ok, but WHY do electrons travel from - to + in my circuit? Why aren't electrons stuck in the wire in the area 'D'?

    If you are pushed and pulled in the same time, would you go left, right or in a circle?
    Why isn't then the current before the resistor stronger than after, since only AFTER the resistor electrons lose energy?
     
  5. Sep 16, 2014 #4

    CWatters

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    The water analogy is far from perfect but consider water flowing through a hydroelectric power turbine. The flow rate coming out is the same as that going in but the water has lost energy. If the flow rate wasn't the same it would accumulate in the turbine causing big problems. Electrons don't like to accumulate in one place either....like charges repel.

    Current is not the same as energy. The amount of power that a hydroelectric power station can generate depends on both the flow rate and the pressure (eg height or head). In the case of electricity power = current * voltage.
     
  6. Sep 16, 2014 #5

    sophiecentaur

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    The chemicals in the battery (or the induced voltages in a generator) force them to go 'against' the natural way they would flow (the way they go through the resistors). They are 'pumped uphill' (A to D) inside the battery and 'roll downhill' (C to B) through the external circuit.
    They cannot build up anywhere because of the strong mutual repulsion.

    PS you must realise that this is a model based on the electrons being otherwise stationary. In metals, they are constantly moving at a range of random speeds in all possible directions - thermal motion. The battery just nudges their mean velocity in a particular direction. The actual drift speed is a mere few mm per second.
     
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