Circuit Analysis and Linear Systems, Part I

Question 1

circuit model

Answer 1

a representation of circuit device made up of ideal circuit elements

• A real circuit does not behave as an ideal linear device but it can be approximated as one or more ideal to produce a mathematical model
• a mathematical model is used to predict the behavior of the circuit with acceptable accuracy for practical applications

Question 2

Kirchoff’s Laws

Answer 2

• fundamental concepts about circuits

- needed for loop and nodal analysis

Question 3

Kirchhoff’s Voltage Law (KVL)

Answer 3

KVL is about conservation of force

• for every action, there is an equal and opposite reaction
• a voltage source exerts force to move electrons
• the sum of the response forces must equal the source

Question 4

DC Circuits

Answer 4

• a voltage source moves electrons in one direction
• the circuit components react to the force in such a way that the electron completes the circuit with no energy, to be accelerated again by the voltage source

Question 5

AC Circuits

Answer 5

• A voltage source moves electrons back and forth
• The effect of the force transfers through the circuit, and the circuit components react in the same way with a DC Circuit

Question 6

voltage divider

Answer 6

works on the principle of an equal and opposite reaction for every action
- voltage sources causes electrons to flow in form of current
- resistors in voltage divider react to force, cause voltage drops
- voltage across resistor 2 is
v2= v (R2/ (R1 + R2))

Question 7

current divider

Answer 7

works on the principle of favoring the path of least resistance
- current is flow of electrons
- flow favors the path of least resistance
-

Question 8

Joule’s law

Answer 8

P= V I = V^2/R = I^2 * R
gives the power P, that is dissipated in
- and individual component with resistance R
- a circuit with an equivalent resistance R

Question 9

resistive power

Answer 9

power in a circuit that is converted to heat

P = dw/ dt = dW/dq dq/dt = V i = i^2 R

Question 10

loop analysis and node analysis

Answer 10

systematic methods for representing circuits as a system of n equations and n unknowns

• loop current method: determining unknown current
• node voltage method: determining unknown voltage

Question 11

loop current circuit analysis

Answer 11

1) select one less than the total number of loops (n-1)
2) Assume current directions for the chosen loops
3) Write Kirchoff’s voltage equation around each loop
4) Solve for the current by using the simultaneous equations generated

Question 12

Node voltage circuit analysis

Answer 12

1. Convert all current sources to voltage sources
2. Choose one node as reference (usually ground)
3. Identify unknown voltages at other nodes compared to reference
4. Write Kirchoff’s current equation for all unknown nodes except reference node
5. Write all currents in terms of voltage drops
6. Write all voltage drops in terms of the node voltages

Question 13

superposition theorem

Answer 13

net current is the sum of all currents caused by each current source
net voltage is the sum of the voltages caused by each voltage sum

Question 14

Thevenin’s theorem

Answer 14

a linear, two terminal network with dependent and independent sources can be represented by a Thevenin equivalent circuit consisting of a voltage source in series with a resistor

Question 15

Norton’s theorem

Answer 15

A linear, two-terminal network with dependent or independent sources can be represented by an equivalent circuit consisting of a single source current source and resistor in parallel

Question 16

maximum power transfer theorem

Answer 16

• A circuit is most efficient when the maximum power available from a source is transferred to a load resistance RL

Question 17

Maximum power transfer theorem

Answer 17

the power transfererred to RL is maximized when the derivative of the load power function taken with respect to RL equals zero

Question 18

two-port equivalent circuit models

Answer 18

• Linear or piecewise linear three- or four terminal devices such as transformers and transistors can be modeled as two-port networks
• A two-port network may be represented by equivalent circuit using a set of two-port parameters, regardless of how the network is actually wired
• commonly used parameters are impedance, admittance, and hybrid parameters

Question 19

impedance model

Answer 19

represents input voltage and output current as functions of input current and output voltage
The network is modeled as
- an input impedance in series with a dependent voltage source and
-an output admittance in parallel with a dependent current source

Question 20

admittance model

Answer 20

represents input and output currents as functions of input and output voltages
The network is modeled as
- an input admittance in parallel with a dependent current source, and
- an output admittance in parallel with a dependent current source

Question 21

two-port hybrid model

Answer 21

represents the input voltage and output current as functions of the input current and output voltage

The network is modeled as

• an input impedance in series with a dependent voltage source, and
• an output admittance in parallel with a dependent current source

Question 22

sinusoid

Answer 22

waveform simlilar to sine function
may be shifted to left or right
frequency, f of sinusoid is reciprocal of period T
angular frequency w, is frequency expressed in radians per second

Question 23

phase shift

Answer 23

• difference between peaks of sinusoids for voltage and current
• due to capacitors and inductors in circuit

Question 24

phase angle

Answer 24

• magnitude of phase shift (in radians)

- by convention, voltage taken as reference

Question 25

phasor

Answer 25

graphically represents a cosine wave as a line in the complex plane contains all the information contained in the time domain diagram of the waveform presents this information in a form that makes it easier to calculate the real and reactive power in the system especially useful for three-phase systems

Question 26

waveform analysis

Answer 26

many characteristics of periodic waveforms can be used to determine other characteristics of the system - average value relates to the charge exchanged by the waveform - root-mean-square (rms) values relate to the power of the waveform - Frequency and wavelength of periodic waveforms are inversely related - phase gives a time comparison of that waveform to the rest of the system, usually as compared with a reference waveform

Question 27

effective value

Answer 27

- a single voltage value that characterizes an alternating waveform for use in power calculations - equivalent to DC voltage with same heating effect - also called root-mean-square value or rms value

Question 28

impedance, Z

Answer 28

- describes the combined effect circuit elements have on current magnitude and phase - units of ohms - a complex quantity with a magnitude and an angle - usually written in polar form

Question 29

series AC circuit

Answer 29

consists of circuit elements connected along single path - the same current flows through all elements - the voltage drop across each element is found from Ohm's law (all calculations are complex algebra) - Kirchoff's voltage law applies to AC circuits (also with complex algebra) - Loop analysis can be used for simple stead-state series AC circuits

Question 30

series RL circuit

Answer 30

- consists only of resistors and inductors in series | - magnitude and phase of impedance found from complex algebra

Question 31

series RC circuit

Answer 31

- consists only of resistors and capacitors | - magnitude and phase of impedance found from complex algebra

Question 32

parallel AC circuit

Answer 32

consists of circuit elements connected so that the same voltage appears simultaneously across all elements - the current through each element can be found from Ohm's law (all calculations are complex algebra) - Kirchhoff's current law applies - Nodal analysis can be used for simple steady-state parallel AC circuits - It is convenient to convert all known circuit element impedances to rectangular admittance form

Question 33

parallel RL circuit

Answer 33

- consists only of resistors and inductors in parallel | - magnitude and phase of admittance found from complex algebra

Question 34

parallel RC circuit

Answer 34

- consists only of resistors and capacitors in parallel | - magnitude and phase of admittance found from complex algebra

Question 35

GLC circuit

Answer 35

- is in parallel RLC circuit - consists of capacitors, inductors, and resistors in parallel - can be lagging or leading

Question 36

transient behavior

Answer 36

- process of changing to a new steady state after a change in configuration of circuit - observed when sources or components are added or removed from a circuit

Question 37

first-order circuit

Answer 37

contains one energy-storing component: one capacitor or one inductor

Question 38

bandwidth

Answer 38

range of frequencies between the half-power points in a circuit or signal

Question 39

half-power points

Answer 39

points where the power is half that of the power at the peak

Question 40

resonant circuit

Answer 40

- at some frequency, called resonant frequency, inductive reactance and capacitance reactance exactly cancel - at resonant frequency, the circuit is purely resistive - Circuits can become resonant when frequency is adjusted, circuit elements are adjusted so that inductive reactance cancels capacitive reactance

Question 41

parallel resonance

Answer 41

also known as band reject filter

Question 42

mathematical transforms

Answer 42

used to analyze time functions by converting them to the frequency domain

Question 43

laplace transforms

Answer 43

used for electronic circuits and control systems