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Homework Help: Why don't Current and Voltage increase (series/parallel)

  1. Dec 2, 2014 #1
    1. The problem statement, all variables and given/known data
    So right now I'm getting lost with series and parallel batteries.

    Current is the change in charge over the change in time. Higher voltages increases the rate at which electrons leave the valence band and move into the conduction band. Wouldn't increasing the voltage also increase the current (as in the case of a battery series) and wouldn't increasing the current actually require an increase in voltage (as in the case of a parallel series.) Why is this not the case? I'm assuming the batteries mess with the resistance somehow, but I'm unsure of exactly how this works. I don't see how there could be any other reason given Ohm's Law.

    Thanks for the help

    2. Relevant equations
    V = IR
    I = V/R

    3. The attempt at a solution
    Practical Electronics for Inventors, Wikipedia
  2. jcsd
  3. Dec 2, 2014 #2


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    Ohms law is valid for conductors. In a conductor, the conduction band is partially filled with electrons without applying any voltage. The voltage gradient accelerate electrons and that increases the current.
    Even in a semiconductor, the voltage gradient accelerates conduction electrons, and the higher drift speed makes the current bigger. The applied voltage usually does not increase the number of conduction electrons. It happens in special cases, in a Zener diode, for example.
    The traditional batteries use chemical reactions between electrolyte and electrode to make the electrodes charged. The charges on the electrodes determine the potential difference between them. It is called the electromotive force, emf. When connecting a load (resistor) between the electrodes, current will flow, but that current flows through not only the external resistor, but also through the electrodes and electrolyte of the battery: They also have some resistance, called internal resistance Ri of the battery. The current in the circuit is I=emf /(Ri+R)
    Connecting batteries in parallel, both of them supplies current for the load.
  4. Dec 3, 2014 #3


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    Correct. I = V/R so if you increase the voltage by putting two batteries in series you get twice the current.

    Correct. I = V/R If you want more current to flow you have to increase the voltage or reduce the resistance.

    I'm not sure what you mean by "parallel series" ?

    If you connect two identical batteries in parallel the voltage is unchanged. If the voltage is unchanged then the current (through the resistor) is unchanged.
  5. Dec 3, 2014 #4
    This is from Wikipedia:

    "Components of an electrical circuit or electronic circuit can be connected in many different ways. The two simplest of these are called series and parallel and occur very frequently. Components connected in series are connected along a single path, so the same current flows through all of the components.[1][2] Components connected in parallel are connected so the same voltage is applied to each component.[3]"

    That's what I don't get. Is the Wikipedia author wrong, or do I not understand what he means by "the same current flows through all of the components" and "Components connected in parallel are connected so the same voltage is applied to each component."

    Thanks for the help
  6. Dec 3, 2014 #5


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    The wiki author has it right. You need to look at some simple circuits. Series and parallel are about as fundamental as you can get so if you don't understand them yet, you really need to dig into the basics.
  7. Dec 4, 2014 #6


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    I know people don't like the water analogy as it's far from perfect but...

    Flow rate = current
    Pressure = Voltage

    Series: Consider a number of water pipes connected in series to make one long water pipe. Water isn't compressible so the flow rate going in one end must be equal to the flow rate coming out. Likewise the flow rate in any of the individual pipes must be the same. If it wasn't the same that would imply water is accumulating at some point and that's not possible. This applies even if there is a constriction in one section. Adding a constriction in one pipe might change the local water pressure and the absolute flow rate but the flow rate in each section of pipe would be the same as every other section.

    Parallel: Consider a number of houses connected to the same water main. If the water main is an "ideal" water main all houses will see the same water pressure. The flow rate to each house depends on use within the house. Adding a constriction to the pipes within a house does not change the pressure that house sees at the incoming main but does change the flow rate to/within the house.
  8. Dec 5, 2014 #7
    That makes sense now. Thank you so much CWatters. Very much appreciated :)
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