There are two
laws necessary for solving circuit problems. For simple
circuits,we have been applying these equations almost
voltages around a closed path in a circuit must
sum to zero. (Kirchoff's law #1), the voltage
drops being negative (following a current through
a resistor), while the gains are positive (going
through a battery from the negative to the
sum of the currents entering a node must equal
the sum of the currents exiting a node. (Kirchoff's
The first law is a simple statement
of the meaning of potential. Since every point on a
circuit has a unique value of the potential, travelling
around the circuit, through any path must bring you back
to the potential. Using the analogy to elevation: If one
hikes from a starting point of a mountain, taking several
paths, then finishes at the same point, the sum of the
elevation changes of each path had better add to zero.
|The second law is
the statment of current conservation mentioned before in the
Ohm's law lecture. For the node on the right, i1=i2+i3.
If all currents had been defined as enterning the
node, then the sum of the currents would be zero.
laws / RC Circuit's index