The Laws of Circuit
- you can learn
and practice by just reading
copyright. Charles Kim 2006
of Freedom or Sort of
- Circuit problem is
eventually asking for or answering two things: voltage
and current. Everything else is just a derivative, that
is, not new but developed from original.. Then we can say
that we have 2 degrees of freedom: voltage and current.
So to speak, we can exercise our freedom with constraint.
For example, for a resistor in a circuit, we are free to
choose the direction of the current OR
the polarity of the voltage across the resistor. Hoever,
we CANNOT exercise the 2 degrees of freedom AT THE SAME
TIME. Because there is the "Passive Convevtion"
like the Geneva Convention on treating POWs. In other
words, if you choose the direction of the current through
a resistor, the polarity of the voltage of the resistor
must be set so that the passive convention is satisfied.
In a voltage source where the polarity is already set, we
have just one freedom of choosing the direction of the
current flowing through the voltage source. In a current
source case, we can choose only the polarity of the
voltage across the current source. In the source case,
remember you exercise your freedom, which means, you do
not have to follow the passive convention. Sources are
NOT passive elements, after all.