Impedance in Electrical Circuits

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Questions and Answers

In a purely resistive AC circuit, what is the phase relationship between the current and voltage?

The current and voltage have no specific phase relationship.

The current and voltage are in phase with each other. (correct)

The current and voltage are 180 degrees out of phase.

The current and voltage are 90 degrees out of phase.

What happens to the current flow in a resistive AC circuit when the instantaneous AC voltage is at maximum?

The current flow is zero.

The current flow is unpredictable.

The current flow is at minimum.

The current flow is at maximum. (correct)

What happens to the current flow in a resistive AC circuit when the instantaneous AC voltage is zero?

The current flow is zero. (correct)

The current flow is unpredictable.

The current flow is at minimum.

The current flow is at maximum.

What is the purpose of a phasor diagram in an AC circuit?

To determine the phase relationship between current and voltage. Signup and view all the answers

What is the relationship between Ohm's law and Kirchhoff's laws in a purely resistive AC circuit?

Both Ohm's law and Kirchhoff's laws are valid in a purely resistive AC circuit. Signup and view all the answers

When calculating circuit values in a resistive AC circuit, what must you ensure before starting the calculations?

That the circuit parameters are expressed in the same terms. Signup and view all the answers

In a purely resistive circuit, the impedance is equal to?

Total circuit resistance Signup and view all the answers

What determines the impedance in a purely inductive circuit?

Total inductive reactance Signup and view all the answers

In a purely capacitive circuit, the impedance is equivalent to?

Total capacitive reactance Signup and view all the answers

What happens to the total circuit impedance (Z) when the frequency varies in an LCR circuit?

Changes due to varying inductive and capacitive reactance Signup and view all the answers

How does the current behave relative to the applied voltage when a series LCR circuit acts capacitively?

Current leads the voltage Signup and view all the answers

What does a series circuit imply in terms of current flow through different components?

Same current flows through all components Signup and view all the answers

What is the phase relationship between the voltage drops across the inductor and capacitor in the series LCR circuit?

180 degrees out of phase Signup and view all the answers

What is the total equivalent reactance (Xeq) in the given series LCR circuit?

$750 \Omega$ Signup and view all the answers

What is the overall effect of reactance on the series LCR circuit?

Capacitive Signup and view all the answers

How can we determine the voltage drop across the individual components in the series LCR circuit?

Using Ohm's law and the known circuit parameters Signup and view all the answers

What is the purpose of constructing a phasor diagram for the series LCR circuit?

To visualize the phase relationships between the voltage drops and the circuit current Signup and view all the answers

What is the relationship between the reactance values of the inductor (XL) and capacitor (Xc) in the series LCR circuit?

They are of opposite phase Signup and view all the answers

Study Notes

AC Voltage and Current in a Resistive Circuit

When the sinusoidal instantaneous AC voltage is zero, the current flow through the circuit will also be zero.
When the instantaneous AC voltage is at maximum, the current flow will be at maximum.
When the voltage polarity changes direction, the current flow's direction will reverse.
The instantaneous values of AC current and voltage conform to Ohm's law.
Peak and RMS values can also be used.

Phasor Diagram of AC Current and Voltage Phases

The magnitude and phase angle of the sine waves can be represented by constructing a phasor diagram.
The voltage and current phasors have a phase angle relationship of 0°.
Current and voltage in a purely resistive AC circuit are in phase with each other.

Impedance in Series LCR Circuits

Impedance (Z) in a purely resistive circuit is equal to the total circuit resistance.
Impedance in a purely inductive circuit is equal to the total inductive reactance.
Impedance in a purely capacitive circuit is equal to the total capacitive reactance.
In a series LCR circuit, the AC source supplies voltage to the circuit at a particular frequency.
Varying the frequency causes both the inductive and capacitive reactance to change.
This changes the total circuit impedance (Z) and the phase angle between the total circuit current (IT) and the applied voltage (VGEN).
At some frequencies, the circuit will act capacitively and the current will lead the applied voltage.
At other frequencies, the circuit will act inductively and the current will lag the applied voltage.

Determining Impedance of Series LCR Circuits

In a series circuit, a single path for current flow exists, and the same current flows through all three components.
Each component has a different voltage dropped across it, with various phase relationships to the circuit current.
Knowing the current and impedance of each component, we can use Ohm's law to determine the voltage drop across the individual circuit components.
From these circuit parameters, we can construct a phasor diagram that shows the phase relationships among the components.
The total equivalent reactance (Xeq) is calculated by subtracting the inductive reactance from the capacitive reactance.

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Description

Learn about impedance in electrical circuits and how it varies in purely resistive, inductive, and capacitive circuits. Understand how impedance is calculated in circuits with a combination of resistance, inductance, and capacitance.