The frequency response of a circuit refers to how the impedance of the circuit varies with frequency. It is important for understanding how the circuit behaves when subjected to different AC frequencies, such as in filters.
What does a phasor diagram represent?
A Voltage and current relationships
B Impedance
C Power factor
D Current division
A phasor diagram is a graphical representation of the voltage and current in an AC circuit. It shows the magnitude and phase of the voltages and currents as vectors, helping visualize the phase relationship between them.
What does complex power consist of in an AC circuit?
A Reactive power only
B Real and reactive power
C Impedance and current
D Real power only
Complex power in an AC circuit consists of both real power (P), which is used to do work, and reactive power (Q), which does not do work but is necessary to maintain the electric and magnetic fields in the circuit.
In an AC circuit, what does the real power represent?
A Stored energy
B Total energy
C Energy used for work
D Energy loss
Real power, measured in watts, represents the energy that is actually consumed and used to perform work in an AC circuit. It is the portion of power that does useful work, such as lighting a bulb or running a motor.
What happens in a circuit when the phase angle between voltage and current is zero?
A No power loss
B Purely capacitive behavior
C Maximum power transfer
D Purely inductive behavior
When the phase angle between voltage and current is zero, voltage and current are in phase, leading to maximum power transfer. This occurs when the power factor is 1, meaning all supplied power is used effectively.
What does a high power factor indicate in an AC circuit?
A High energy loss
B Efficient power usage
C Low impedance
D High reactance
A high power factor indicates that most of the power supplied is being used for useful work (real power), with minimal waste in the form of reactive power. It reflects the efficiency of energy usage in the circuit.
What is the relationship between voltage and current in a purely resistive AC circuit?
A 180° phase shift
B 90° phase shift
C In phase
D Current leads voltage
In a purely resistive AC circuit, the voltage and current are in phase with each other. This means that the voltage and current reach their maximum and zero points simultaneously. This results in no phase shift, and the power factor is 1, indicating maximum efficiency.
What is the effect of increasing frequency on the inductive reactance of a circuit?
A Increases
B No change
C Becomes constant
D Decreases
Inductive reactance increases with frequency because it is directly proportional to the frequency of the AC signal. As the frequency increases, the inductor opposes the current more strongly, resulting in higher reactance.
What does the impedance of a purely capacitive AC circuit depend on?
A Voltage
B Current
C Resistance
D Frequency
The impedance of a purely capacitive AC circuit is inversely proportional to the frequency. As the frequency increases, the impedance decreases, allowing more current to flow through the circuit. It is given by Z = 1 / (jωC).
In a series RLC circuit, how does the total impedance change as the frequency increases?
A Remains constant
B Increases
C Becomes zero
D Decreases
In a series RLC circuit, the total impedance increases as the frequency moves away from resonance, especially if the circuit becomes inductive. The impedance is a combination of resistance and reactances, and their effect grows with frequency.
What does the reactance of a capacitor in an AC circuit depend on?
A Capacitance
B Inductance
C Resistance
D Frequency
The reactance of a capacitor in an AC circuit is inversely proportional to the frequency. As the frequency of the AC signal increases, the capacitive reactance decreases, allowing more current to flow through the capacitor.
What is the purpose of using phasor diagrams in AC circuit analysis?
A Analyze current division
B Calculate impedance
C Represent voltage and current relationships
D Show power loss
Phasor diagrams are used to visually represent the phase relationships between voltages and currents in an AC circuit. They help understand the magnitude and phase differences between voltages and currents, which is crucial for analyzing power and impedance.
In AC circuits, what is reactive power responsible for?
A Maintaining magnetic fields
B Power loss
C Doing work
D Increasing efficiency
Reactive power (measured in VARs) does not perform any useful work but is essential for maintaining the magnetic and electric fields in inductive and capacitive components of the circuit. It is required for energy storage in the system.
What is the role of complex power in an AC circuit?
A Determine current
B Measure impedance
C Calculate voltage
D Analyze real and reactive power
Complex power combines both real power (P) and reactive power (Q) in an AC circuit. It is represented as S = P + jQ, where P is the real power in watts, and Q is the reactive power in VARs. This helps analyze the total power flow in the circuit.
What happens when the impedance of a circuit is purely resistive?
A Phase shift is 90°
B Current and voltage are in phase
C Current is maximum
D Power factor is zero
When the impedance of a circuit is purely resistive, the voltage and current are in phase, meaning they reach their peak and zero values at the same time. This results in a power factor of 1, indicating maximum efficiency.