Chapter 23 Alternating Current Circuits

Capacitative Reactance

-is a measure of a capacitor's opposition to AC (alternating current) -measured in ohms, like resistance but reactance is more complex than resistance because its value depends on the frequency (f) of the electrical signal passing through the capacitor -is not a fixed value like resistance and instead varies with the applied frequency

What is the average power used by an inductor in an AC circuit?

An inductor alternately absorbs and releases energy for equal periods of time. this means that the average power (and, hence, the average energy) used by an inductor in an ac circuit is zero

How does the capacitive reactance depend on frequency?

As frequency increase the capacitive reactance decreases, meaning that the capacitor offers little resistance to AC current. When frequency decreases the capacitive reactance increase and the capacitor provides a high opposition to the motion of charges.

Resonance is determined by what factors?

Capacitance and inductance

In a series RCL circuit at resonance, does the current lead or lag behind the voltage across the generator, or is the current in phase with the voltage?

In phase because XL=XC and it only depends on the resistor which is in phase

Do capacitors use power?

NO

Are resistors frequency dependent?

No

At resonance impedance is equal to

R

How does the inductive reactance depend on frequency?

The greater the frequency the greater the inductive reactance (a large opposition to the alternating current. -The smaller the frequency the smaller the inductive reactance and the less opposition there is to changing current flow.

Describe the resistance of a capacitor at low and high frequencies

at high frequency: capacitors offer so little resistance they act like straight wire at low frequency: they offer so much resistance it is like a gap in the circuit

The resonant frequency is determined by

by the inductance and capacitance but not by the resistance

At low frequencies what element dominates and provides the greatest R?

capacitors

At low frequencies capacitors act like _____ and inductors like _______

capacitors act like gaps (infinite resistance) inductors act like straight wires

At high frequencies capacitors act like _____ and inductors like

capacitors act like straight wires inductors act like gaps (infinite resistance)

At resonant frequency ____ is at a maximum and ____is at a minimum

current is at a max impedance is at a minimum

At high frequencies what element dominates and provides greatest R?

inductors

As you increase capacitance what happens to the capacitative reacatance?

it decreases

At resonance when resistance is large there is

less current at maximum

The rms current is at a _______ when the impedance is a minimum

maximum

Does a resistor affect the resonance frequency?

no

Capacitive reactance depends on

on the frequency of the AC generator

What parts of a circuit are not are affected by AC current?

resistors (act just like they normally would) capacitors and inductors are affected

What is the average power used by a capacitor?

the average power used by a capacitor in an ac circuit is zero because power alternates between positive and negative values for equal periods of time

Impedance

the equivalent resistance ("total opposition to charge flow") for an AC circuit measured in Ohms

Impedance depends on

the frequency of the AC generator

At resonance describe XL and XC

they are equal

Describe voltage and current for a resistor

they are in phase

The resistance in a series RCL circuit is doubled. (a) Does the resonant frequency increase, decrease, or remain the same? b) Does the maximum current in the circuit increase, decrease, or remain the same?

a) remains the same b) decrease

An inductor alternately absorbs and releases energy for _____ periods of time. What does this mean about the power being used by the inductor?

equal periods of time the power must then be 0

Does the value of a resistor change with frequency?

no, it has the same value at every frequency

What components in an RLC circuit use power?

only resistors capacitors and inductors DO NOT

For AC current what uses power?

only the resistor bc voltage and current are in-phase inductors and capacitors don't use power because current and voltage are out of phase

If you double resistance in RLC circuit what happens to the resonant frequency and the max current?

resonant frequency stays the same max current decreases

Describe voltage and current for an inductor

they are out of phase current lags behind voltage by 90 degrees

What happens to a capacitor in AC current circuit?

-polarity of the voltage applied to the capacitor continually switches back and forth -inresponse, charges flow first one way around the circuit and then the other way (aka AC current) -charge flows continuously in an ac circuit containing a capacitor

Phasor

-rotating arrow that symbolizes the magnitude and phase of a value -rotate CCW -vertical component is the instantaneous current or voltage

Inductive Reactance

The opposition to current flow by an inductor in an AC circuit.

Describe voltage and current for a capactior

they are out of phase current leads voltage by 90 degrees

Inductor

A coil of wire that creates a magnetic field when current passes through it -stores energy in a magnetic field when electric current flows through it