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Circuit terminology

Definition of circuit terms: element, component, node, branch, mesh, and loop . Created by Willy McAllister.

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  • piceratops sapling style avatar for user Kanishk
    what is the difference between a mesh and a loop ?
    (16 votes)
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    • spunky sam orange style avatar for user Willy McAllister
      A loop is any closed path around the circuit. You are allowed to visit each element only one time (you are not allowed to create a figure-8 by going through an element twice). A mesh is a loop, with the restriction that a mesh contains no other loops. We focus on meshes because the number of meshes is exactly right for getting the proper number of independent equations.
      (26 votes)
  • female robot grace style avatar for user Anna
    Which form of current is more dangerous? AC or DC?

    I have heard several contradictory things relating to this. Here is what I have heard:

    "AC has a higher voltage and thus higher number of amps. Even 1 amp can kill you. AC is more dangerous."

    "DC typically has a lower voltage and its amps are usually very small(milli or even microamps). However DC often leads to longer exposure and thus is more dangerous."

    "AC is less dangerous because its sine wave makes your muscles twitch and force you to let go."

    "DC is more dangerous because even though it takes more volts and amps to kill you than AC, it makes your muscles continuously contract and you might not be able to let go of the DC circuit."

    So which one is more dangerous, AC or DC? I probably wouldn't have to worry about handling a DC circuit even at 12-24 volts because the amps are so small. I might get pain but I doubt I will get continuous contraction. I mean the resistance of human skin is anywhere from 1 million to 15 million ohms according to some of the sources I got this AC vs DC info from. And with amps that are already very small, that much resistance means practically nothing gets through me.
    (10 votes)
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  • male robot hal style avatar for user Jesse Arias
    How do we know where to start and end the loop?
    (8 votes)
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    • spunky sam orange style avatar for user Willy McAllister
      Loops don't have a start or end, they are just loops. When you draw a loop on a circuit, you get to choose where to put your pencil down first. When I do it, my habit is to start in the lower left and draw in the clockwise direction. It's not a rule, just a habit. When you get to the circuit analysis method called the Mesh Current Method, you will learn how to "travel around a mesh". (A mesh is a kind of loop.) With this method, you have to select a starting point (the "start of the loop") and direction to travel. Again, my habit is the same: start at a point near the lower left and go around clockwise.
      (10 votes)
  • leaf green style avatar for user Derek
    At the first loop is illustrated as extending to the end of the second mesh, but I don't understand why that is. My intuition is that there would only be 3 loops, but we were told to take the 3 loops given to us and add it to the number of mesh to get the loops. Why is this? It doesn't seem intuitive to understand, and I don't feel as if I was given really any information regarding what a loop is or even how to adequately count them. Thanks!
    (3 votes)
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    • mr pants teal style avatar for user Robert
      Think of the meshes as minimal examples of loops, in the sense that they don't "contain" smaller loops inside of them. I think you may see that the meshes, being already covered, weren't also listed as loops until the end, where we we're told to count those three meshes in as well when counting loops.
      (7 votes)
  • blobby green style avatar for user Steven
    So in an ideal wire, the current is always infinite if the voltage is non-zero? (Ohm's law)
    (2 votes)
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  • winston default style avatar for user Shubam Vennu
    What is the difference between a mesh and a loop
    (3 votes)
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    • spunky sam orange style avatar for user Willy McAllister
      A Loop is any closed path around a circuit (not counting figure-8 paths).

      A Mesh is a kind of loop. It is a little simpler. It has the property that it goes around the 'open windows' of a circuit.

      Why do we make this distinction? Mesh vs Loop comes up in the section on DC Circuit Analysis. There is an important analysis technique called the Mesh Current Method, based specifically on the definition of a Mesh.

      You will get to that in a little while. For the moment just remember these two words have similar meanings, and the small difference will become important later.
      (4 votes)
  • hopper happy style avatar for user Waco Glennon
    At around 5 minutes, Willy starts the discussion about "mesh" and "loop". What is the practicality of knowing the number of meshes or loops?
    (2 votes)
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  • starky seedling style avatar for user mohd1342
    what is the difference between nodes and branches?
    (1 vote)
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    • blobby green style avatar for user Erick Robles
      The way i see it, do not confused a "wire" with a "branch". A wire is arbitrary, it is basically a material that we need to make up a circuit. That said, once we have laid out how our circuit will look like, a branch is any path in the circuit that has a node at each end; a path connecting nodes.
      (4 votes)
  • aqualine tree style avatar for user manisha sinwar
    Is a voltage source a branch too ? if , it is i am confused about it because the teacher didn't said its the first branch .
    (1 vote)
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    • duskpin ultimate style avatar for user Didi
      Yes, Problem 2 is a branch example and under "explain", you can see the voltage source is a branch too. Also, the definition of branch says, "A branch is an element (resistor, capacitor, source, etc.)" so a voltage source is included.
      (3 votes)
  • leaf green style avatar for user Jack Wu
    Good morning! I really wish someone can answer my question: What is the difference between mesh and loop? Or is Loop just larger version of the mesh? Thank you!
    (1 vote)
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Video transcript

- [Voiceover] In this video, we're gonna talk about some terminology that we use to talk about, how circuits are put together. In previous videos, we've talked about the components, or the elements, that are used to make up circuits. So, for an example, resistor, capacitor, and inductor, are circuit components. We also call those elements. In addition, we have some sources, like a voltage source, or for example, a current source. Those would be the components... Or elements of a circuit. Now, we're going to start assembling these things into circuits, and we need a few more words to talk about. Here's some circuit components, that are laying out on the tabletop, and we're gonna connect those up with a wire. For example, I could connect this one to this one, with this yellow, ideal wire. An ideal wire has zero resistance, and it's perfect everywhere. This forms a junction, between these two components. That is called a node. Node is the word for junction, mean the same thing. That's what a node is. If I connect up these two other components, I still have one node, because I have one junction, that's the same voltage everywhere. That's what a node is. We're gonna go over to this circuit here, and we'll identify the nodes. This is a little more normal looking, tidy circuit. Here's a junction, right here, between a resistor, and this voltage source. So that's one node. If I move over here, I see resistors connected together by ideal wires, so that forms one single node, like that. That's our second node. Down below, same sort of thing. I see an ideal wire, connecting the resistors, and the source, so I can color that in. That's node number three. This circuit has three nodes. Now what's connecting the nodes? The thing that's connecting the nodes, is called a branch. A branch is the same things as an element. We'll count the branches, or elements, in this thing. This voltage source, connects the third node to the first node, so that's one element. This resistor connects node one and node two, so that's the second branch. This resister connects node two and node three, so there's the third branch. And this resistor, with a separate current, also connects those two nodes, so that's the fourth branch. This circuit has one, two, three, four elements in it, and it also means, it has four branches. Four branches. That's what a branch and a node are. I'm gonna move the picture over a little bit, so that we can do this again, on a little more fancy circuit. First thing we're gonna do, again, just to repeat the process, we're gonna count the nodes. Here's a junction between a resistor and a source, here's three resistors, connected by a perfect wire, so that's the second node. Here we find three more resistors, connected by a perfect wire, there's the third. Down here, we have, there's a junction, between two resistors, so that's our fourth node. Finally, we have this node here, connecting these four elements, with one node. This is sometimes called a distributed, a distributed node, when it's all spread out on the page like that, but it's still just one node. So this circuit has five nodes. If we count up the elements, that will tell us how many branches there are. One element, two, three, four, five, six, seven? Seven elements. Alright, there's our two key words. Elements and nodes. Now, I'm gonna quickly move again, down. Bring in another circuit here. We're gonna talk about the idea of a mesh. The other thing we're gonna about is the word, loop. The word mesh comes from screen doors, or screens that you put on your windows, to keep the bugs out. If I draw a screen, like this, this is what it looks like. A bunch of crossing wires. This little space right here, that little gap, is called a mesh. That's what that word comes from. We're gonna find the meshes of our circuit. What we look for, here's the branches, and the mesh, it is a kind of a loop, that fills up this open space. This circuit has one mesh, two mesh, three meshes. That's how that looks. To draw a mesh, you start on a node, you go through elements, until you come back to where you started. That's how we did those three, and they fill the open windows of the circuit. This circuit has three meshes. A mesh is a loop, and we can have other kinds of loops, too. They don't have to be just the ones that fill the windows. In general, this circuit has other loops, and we'll identify some of those. Let's just start at one of these nodes here, and go around like that. This is a loop. I could draw other loops in here, we'll make them all different colors. There's a loop, if I start right here, I can draw a loop through these elements. Finally, if I have a sharp eye, there's one more loop in this circuit. Let's just start right here, and it actually goes all the way around the outside. This circuit has three, actually, if I add them together, this has three loops, that I drew here, plus the three loops that were the meshes. This circuit has six loops. Circuits always have a lot of loops, and so, usually, we don't talk about these. More often, it's more organized and straightforward to talk about how many meshes are in a circuit. Alright. That does it for this video. We got mesh and loop, we talked about components and elements... And we finished up, with the idea, also, of nodes and branches. That'll do it. There's our new vocabulary, for talkin' about circuits.