Two active(有源)models
Three passive(无源)models
V0 = E
Is =
When R0 = 0, V = E, the source is called ideal voltage source.
R0 = 0
The ideal current source:
(1) Current -- i(t), I ---- (A, mA, μA...)
The net time-rate of transference (传递) of charge is referred to as the flow of current.
(2) Energy (or work) -- w(t) (J)
: Electron: negatively charged
Direction of current: is defined as the flow direction of positive charge.
The relative (关联) reference directions
The reference arrow for the current variable enters the terminal, which is identified by the plus sign of the voltage reference polarity markings.
p(t)>0 the power absorbed by the element.
The resistor is a passive element that cannot deliver power or store energy.
We define a "short circuit" as a resistance of zero ohms.
We define a "open circuit" as an infinite resistance.
Suppose that we start at one node in a network and move through a simple element to the node at the other…, if no node was encountered more than once, then the set of nodes and elements that we have passed through is defined as a path(路径).
Kirchhoff's current law --KCL
The algebraic sum of all the currents entering any node is zero.
If the node at which we started is the same as the node on which we ended, then the path is a closed path(闭合路径)or a loop(回路).
The three equivalent equations
The algebraic sum of all the currents entering any node is zero.
9 –( – 2)+ I3 + 8 = 0
I3 = –19 A
Kirchhoff's voltage law--KVL
KVL:
A practical current source is defined as an ideal current source in parallel with an internal resistance Rsi.
Conditions of equivalence:
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