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Helping me to understand the difference between pd of a source and a component

  1. Nov 3, 2012 #1
    Hi, I've recently been reading up on circuit electricity and as the title states have found difficulty understanding the difference between pd of a source and a component from the textbooks I've been reading.

    So far I am to believe that the pd of a circuit is directly proportional to its current, fine - I can understand this as higher pd = more energetic electrons so they move around the circuit faster hence higher current... the pd of the battery can be seen as a sort of 'driving' force on the electrons.

    However, when defining the pd I am told it is how much energy per unit charge used in passing through a certain component. - The battery supplies the pd and the electrons 'spend' it passing through the components. So the pd of the component can be seen as just how difficult it is, or how much energy is required for a charge to pass through it.

    My misunderstanding started when imagining a series circuit in which the pd of the battery was doubled. Since I know the equation V=IR and understand that the pd of the battery is like its driving force I can see that the total current of the circuit would double also.

    What I want to know is why the sum of the pds across the components must now add up the the new total pd when the resistance has not increased so the electrons would have no more difficulty in passing through them. Wouldn't the electrons not just be supplied this new doubled amount of energy but then use the same amount as before with half left over? Why does the increase of current seemingly make the electrons need more energy to pass through the same components that they already passed through for half the energy?!

    I am sorry if these questions are stupid or I am misunderstanding on some fundamental level but please understand I don't have a teacher I am purely studying this topic for the first time on my own.


    *EDIT: after some thought I have been able to narrow down my problem to the following statement : 'the sum of the voltage drops across each component of one complete loop of the circuit is equal to the supply voltage.'

    If I accept the above as fact it all makes sense, however I still feel that without explanation I can't really understand why this is.
    Last edited: Nov 3, 2012
  2. jcsd
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