| Circuits |  |
An electrical circuit is where all the fancy electrical stuff happen! A circuit can be as simple as a battery connected to a lamp or as complicated as a computer. Circuit is defined as below:
“A closed loop consisting of two or more electrical components connected with wires is a circuit.”
The closed loop part is very important, as an open loop cannot result in a circuit and doesn’t have any electrical functionality. The loop has to be closed so that the electrical current can flow in the loop. An electrical component is an element with a number of terminals, which has some effects on the passing electricity through it. Therefore is used for it's behavior to achieve a purpose in a circuit. A circuit component can also be a mixture of other smaller components. Figure below shows a simple circuit consisting of two components: a battery and a lamp.
The two circuits shown in the figure below are connected with one wire. The loop between these two is not closed and therefore actually they are two independent circuits, because with only one connection, electrical current can't flow in-between the two. Remember that simply when current flows in one direction, it needs another path to return.
There are some important terms in a circuit that are used a lot such as branch, short circuit, node, mesh, parallel and series components and super node. This terms are explained below.
Short Circuit
You hear this term in SiFi movies when they want to destroy an evil robot by short circuiting it! It simply means connecting two electrical components together with a link (a wire). The short circuit is not a component, because virtually it has no effect on the value of current passing through it but it only allows it to pass. It means a short doesn’t have any resistance, capacitance, inductance and … Therefore the Voltage across a short is always zero no matter what the shape or length of a short is. Shorts in a circuit are shown with lines and no matter how you draw it, the result is the same. The lines in the figure above are shorts between the two components.
In SiFi movies a short circuit sounds like a destructive term, because by that they mean short-circuiting between two points of a circuit, such as between the power lines so that the huge power passing through the short burns the evil robot! I guess everyone has seen a big spike once in a while, which is quite dangerous for robots and humans!
Node
A circuit node is where two or more components are connected together with shorts. Figure below shows an example of a simple node. The lines are shorts that are connected to the other components in the circuit. A node acts like an intersection of flowing currents.
Similar to shorts, nodes have no electrical properties of their own and are only a mean to connect circuit parts together. Always remember this: Two nodes connected together with a short are one, they are just there to confuse you! Because the length of a short doesn't matter and you can put these two nodes it the same spot, making just one node, as shown below:
Always a bullet is put on where two or more wires intersect. This way one understands that those wires are connected in the location of the bullet and can distinguish them from two wires which are simply passing on top of each other. Note that not always the number of bullets are equal to the number of nodes, as also shown in the figure above.
Branch
A circuit branch is between any two nodes, consisting of one or more components connected in series. There would be no other branches connected in-between the two nodes of one branch. Figure below shows an example of a branches between nodes N1 and N2.
Mesh
A mesh in a circuit is any close loop starting and ending with the same node, not passing any node or branch twice. Figure below shows three different meshes for a circuit.
Components in Series
Components are located in series when they are connected back to back and to every node between the components only two components are attached. The example of a branch above is also an example of components in series between the two nodes N1 and N2. Figure below shows an example where components C1 and C2 are in series while C2 and C3 or C4 are not.
Components in Parallel
Basically, all the branches that are connected between the same two nodes are in parallel, and as said before, every branch can include one or more components in series. Figure below shows an example of three parallel branches. You understand now why both circuits below are the same. Because the length of a short is not important, the short lengths between the two bullets above or below the branches can be zero, resulting in the circuit on the left. So remember, no matter how many bullets you have on shorts connected together, all make only one single node.
Also figure below shows an example where there are no components or branches in parallel, as there are no branches that share the same two nodes.
Super Node
Super node is mostly used to simplify calculations to solve for a circuit parameters. To understand this term better you need more information and therefore it is described at the end of the Krichhoff Laws section.
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| Written by: Mehdi Sadaghdar | |