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Homework Help: What is a node exactly?

  1. Jan 29, 2014 #1

    How can one spot a node?

    I know that the blue dots are nodes but why isn't the red dot a node?

  2. jcsd
  3. Jan 29, 2014 #2
    All three dots are nodes.
  4. Jan 29, 2014 #3


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    Gold Member

    Cool it with the massive fonts. It's SCREAMING and is not necessary.

    A node is just any place where two or more elements come together. As scott said, all three colored dots are nodes, and I would add that the ground is a node as well.
  5. Jan 29, 2014 #4
    I didn't create the image, its just a screen shot from my university lectures. I apologise.

    When you say ''element'' do you just mean three ''branches'' of the circuit?

    If so, why is there a node at the place of the red dot in the image below?


  6. Jan 29, 2014 #5


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    Staff Emeritus
    Science Advisor
    Homework Helper

    A node, in this context, is any point in the circuit at which you want to find the current, voltage, or some other property.

    Topologically, in the second circuit, the red node with the (-) attached is equivalent to the ground.
  7. Jan 29, 2014 #6


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    Staff: Mentor

    Circuit elements (or components) are joined together by wires. Where wires from components connect there is a node. Every wire in the circuit is part of some node.

    An "element" just means a circuit component, such as a voltage source, current source, resistor, capacitor, or inductor. You can define a node any place two or more such elements join. Sometimes it is convenient to define nodes in the middle of branches because you happen to be interested in finding the potential there. Otherwise such nodes are considered to be "non-essential" nodes, and aren't required for finding the potentials at other "essential" nodes.

    The "V" node in the second circuit is an example of a non-essential node. The two resistors (2 and 6 Ohms) comprise a single series branch between nodes V1 and V2. Those resistors could easily be combined into a single 8 Ohm resistor and one could proceed to find the potentials of node V1 and V2 without difficulty (and with one less node equation). The node V was introduced, apparently, because it was desired to find the potential there.
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