AC_Analysis Flashcards
(39 cards)
What is a inductor?
What is inductance?
An inductor is composed of a coil of wire wound around a supporting core.
The inductor voltage is determined by the magnetic field which in turn is produced by the current flowing around the coil.
The voltage is directly proportional to the inductance and the rate of change of the current.
So a constant current will produce 0 V across an inductor, like a short circuit
Why can a current not change abruptly across a inductor?
Doing so would require or produce an infinitely large voltage which cannot exist in practice.
What is a capacitor?
A capacitor is composed of two conductors separated by an insulator** or **dielectric material.
A voltage applied to a capacitor creates opposite electrical charges on the two conductors which in turn generate an electric field between them
What is capacitance ?
Eq?
The separation (d) and area of the conductors (A), and the permittivity of the insulator/dielectric determine the capacitance in Farads (F).
Voltage Current relationship of a capacitor?
The current is directly proportional to the capacitance and the rate of change of the voltage.
So a constant voltage will produce zero current into or out of the capacitor’s terminals, like an open circuit.
Why can’t the voltage change abruptly across a capacitor?
It would require or produce an infinitely large current which cannot exist in practice.
dv would be a lot larger than dt, meaning that i has to be really large.
The Phasor ?
Is a complex number representing a sinusoidal function
Phasor Question
Why is e-j(pi/2) = -j ?
e-j*θ = cos(θ) - j*sin(θ)
e-j(pi/2) = cos(pi/2) - j*sin(pi/2)
e-j(pi/2) = -j(1)
e-j(pi/2) = -j
Inductor Voltage-Current Relationship Eq?
Capacitor Voltage-Current Relationship?
What is Impedance ?
The impedance is simply the ratio of the voltage phasor to the current phasor of any circuit element or terminals.
Because of the presence of j and ω, the impedance of the inductor and capacitor is complex and frequency dependent.
For a capacitor and Inductor, state what leads what.
From the equation V = jωLI, the inductor voltage leads its current by 90˚
From the equation V = I / jωC, the capacitor current leads its voltage by 90˚.
What is the impedance of a resistor?
A resistor has an impedance which is equal to its resistance and therefore purely real.
How do you find the current phasor of a circuit?
You first convert the voltage to its phasor equivalent.
Next, you find out the individual impedances of the circuit elements, add them and then use V/I = z to find the current phasor.
How would you find voltage phasor of a capacitor and then find the stead state eq?
Find voltage phasor using V = I / jωC
The steady state can be found by knowing omega, and plugging the values back in
v = Vm * cos(ω*t + ϕ)
By finding the impedance at terminals a and b, calculate the current phasor of the following circuit.
What are the two parts that make up impedance and what are they called ?
The impedance Z is in general a complex quantity…
…where the real part is the resistance and the imaginary part is the reactance. Therefore the inductor has a positive reactance while the capacitor has a negative reactance.
Why does a capacitor have negative reactance?
And always seem to have negative impedance?
What is admittance?
The admittance (Y) is the reciprocal of the impedance.
The real part is the conductance and the imaginary part is the susceptance. Therefore the capacitor has a positive susceptance while the inductor has a negative susceptance.
What are filters?
Filters are frequency-selective circuits that allow you to pass or attenuate different electronic signals based on their frequencies.
Filters are described by their complex transfer function H(j ω) which is the ratio of the output to input voltage phasors and is therefore a function of the signal frequency ω.
complex transfer function vs. frequency of a low pass filter?
complex transfer function vs. frequency of a High pass filter?
complex transfer function vs. frequency of a bandpass filter?
