The red spheres represent positive current, which is in the opposite direction of electron current.
In this video we will discuss how to find the voltages and currents of large and complicated electric circuits.
This procedure can be used regardless of how many resistors, voltage sources, and current sources are present.
The first step is to pick a point on the circuit that will be defined as zero volts.
All other voltages will be defined in reference to this point.
This voltage source creates a 7 volt difference between its terminals, and we therefore know that this point is at 7 volts.
This point is at an unknown voltage, which we will label "Va."
"Va" will be one of the variables we will have to solve for.
The "two volt" voltage source creates a 2 volt difference between its terminals, and we therefore know that this other point has a voltage of "Va" plus 2 volts.
These points are at an unknown voltage, which we will label "Vb."
The "8 volt" voltage source creates an 8 volt difference between its terminals, and we therefore know that this point has a voltage of "Vb" plus 8 volts.
We have now labeled all the voltages in this circuit.
Let’s now label all the currents.
At each point in the circuit, the current entering is equal to the current exiting.
For example: i2 = i8 + i3.
The current through a resistor is the voltage drop across it, divided by the resistance.
i2 = [ (Vb+8) - (Va+2) ] / 1
i8 = [ (Va+2) - (Vb) ] / 2
Let’s now return to the equation stating that the current entering is equal to the current exiting.
We can now substitute the expressions we calculated for "i2" and "i8."
Let’s now repeat this procedure for every point in the circuit.
We now have 6 equations with 6 unknown variables.
We can use algebra to solve for the unknown variables.
In this way, we can solve extremely large and complicated circuits, no matter how many resistors, voltage sources, and current sources are present.
Much more information is available in the other videos on this channel.
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