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Circuit analysis -- Voltage question

  1. Nov 15, 2015 #1
    hello,

    i have a question regarding the way we represent information on circuit diagrams.

    The first is to do with representing output voltages: 12243789_1651989198375566_1915806819_n.jpg

    is V out always simply representing the voltage of whatever lies between/trapped between those two horizontal lines? Also, i see a lot of diagrams like this and am asked to determine v out. However, im not sure whether or not current would flow into those horizontal lines protruding out to those 2 nodes. I dont know whats been connected in there... do i need to know? does current "split" at that top junction?

    regards

    james.
     
  2. jcsd
  3. Nov 15, 2015 #2

    CWatters

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    In short yes.

    If the output nodes are NOT connected to anything then no current flows "out to those nodes". In the drawing you posted the output is open circuit (nothing connected to the output) so the current does not split at that top junction. It all goes through the diode. Vout would be known as the "open circuit output voltage". In your example the open circuit output voltage would be equal to the forward voltage drop of the diode. Typically about 0.7V for small silicon diodes.

    In other circuits there might be something connected to the output and then that has to be taken into account. For example if the output terminals were connected together with a wire we would say the output has been "short circuited". The output voltage would be zero but there might be current flowing in the wire. This would be known as the "short circuit output current". In your example the short circuit output current would be 5/2500= 2mA
     
  4. Nov 15, 2015 #3
    thank you for clarifying- i do have one other question though,

    when you say there could be a wire between the terminals, why does that imply the V out would be zero?
     
  5. Nov 15, 2015 #4

    sophiecentaur

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    A true short circuit has no PD across it, whatever current is passing through it. R=0 so IR = 0
     
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