Circuits #1
What is current in an open circuit?
0
What is resistance in a short circuit?
0
What is voltage in a short circuit?
0
How do you add resistors in parallel?
1/Req=1/R1+1/R2...
What is the shape of an independent source?
A circle
What is a supernode?
A combination of two or more nodes in nodal analysis, with a voltage source inside
What is a node?
A junction between two or more circuit elements, made of interconnected perfect conductors
What is voltage?
A measure of the energy needed to move one unit of charge between two points on a circuit
What is a loop?
A path where one node, which is both the first and the last, is passed twice
What information do you need to know a charge?
A quantity and a direction
What is a path?
A route between nodes where no node is crossed more than once
What is the shape of a dependent source?
A square
When doing nodal analysis, which voltage to subtract from which?
After assuming a current direction for your overall sign, voltage at the tail of the arrow-voltage at the head of the arrow
How do you add resistors in series?
Algebraically
What is the SI unit for charge?
Amperes, Columbs/second
What is a current source?
An element that provides a constant current regardless of the voltage across it
What is a voltage source?
An element that provides a constant voltage regardless of the current through it
What is true of the power absorbed and emitted by each element in a circuit?
By power conservation, they must all add algebraically to 0
What can you do with the equation for power and ohm's law?
Combine them to calculate power using different kinds of information
What are the steps of nodal analysis?
Find all the nodes, choose one to be the ground, assign a node voltage to each node, write KCl relations for each node using the same sign conventions in terms of the voltages, then solve for the voltages
What is the equation for current division across parallel resistors?
I1=[R2/(R1+R2)](Itot)
What is resistance in an open circuit?
Infinite
What is the equation for power in terms of voltage and current?
P=±V(I), depending on whether passive sign convention holds
What information do we need to know a voltage?
Quantity and polarity
What is the alternate equation for Req in parallel?
Req=(R1R2)/(R1+R2)
What happens to Req if one of the "resistors" in parallel is a short circuit?
Req=0
What does Kirchhoff's current law state?
The algebraic sum of currents entering and leaving a given node is 0
What does Kirchhoff's voltage law state?
The algebraic sum of voltages around any loop is 0
What is required for a parallel connection?
The elements involved must share two nodes
What is current as a rate of change?
The rate of change of current over time, dq(t)/dt
What is power as a rate of change?
The rate of change of energy over time, dw(t)/dt
What is a Siemen? (S)
The unit for conductance, the opposite of resistance, =1/Ω
What do you need to be careful of in nodal analysis when a node is not connected to the ground?
The voltage you calculate will be relative to nearby voltages, not the ground, which means to determine the actual node voltage you will need to subtract other voltages
What is required for a series connection?
Two circuits should be connected back to back without another current path available
What is the equation for voltage division across series resistors?
V1=[R1/(R1+R2)](Vtot)
What does ohm's law state?
V=±RI, depending on passive sign convention
What is D.C. voltage?
Voltage that is constant with respect to time
What is A.C. voltage?
Voltage that varies with respect to time
What do we mean by an equivalent resistor?
We mean that from the perspective of the two nodes at either end, V and I are the same
When does a voltage-current pair conform to passive sign convention?
When the current moves from the positive to the negative of the voltage
Will KVL and KCL work regardless of which directions you assume?
Yes
How do you use supernodes?
You write a KCL equation for them, involving each current coming into the whole thing, then you write an equation using the internal voltage source saying that all of the node voltages for node included in the supernode must add to give the voltage of the internal voltage source
What is voltage as a rate of change?
change in energy/change in charge
