What is the primary function of power analysis in AC circuits?
A Determine frequency
B Calculate power
C Calculate current
D Measure impedance
Power analysis in AC circuits is used to calculate the real power, reactive power, and apparent power. It helps determine how much energy is being consumed, stored, or transferred in the circuit.
What is the main purpose of energy storage in a capacitor?
A Store energy
B Store charge
C Store current
D Store voltage
A capacitor stores energy in an electric field between its plates when charged. The stored energy can later be released when needed to stabilize voltage or smooth power supply fluctuations in the circuit.
What is resonance in an AC circuit?
A Maximum current flow
B Voltage drop
C Minimum impedance
D Current lag
Resonance in an AC circuit occurs when the inductive reactance and capacitive reactance cancel each other out, resulting in minimum impedance. This allows maximum current to flow through the circuit.
What does the power factor in an AC circuit represent?
A Voltage variation
B Efficiency of power usage
C Impedance ratio
D Frequency response
The power factor represents the efficiency with which electrical power is used in a circuit. It is the ratio of real power to apparent power. A power factor of 1 indicates that all power is being used effectively.
How is real power in an AC circuit calculated?
A Voltage × Current × Impedance
B Voltage × Impedance
C Voltage × Current × Power Factor
D Current × Power Factor
Real power (P) in an AC circuit is calculated by multiplying the voltage, current, and power factor. The power factor accounts for the phase difference between current and voltage, determining the usable power in the circuit.
What happens to the power factor if the load is purely resistive?
A Becomes 1
B Increases linearly
C Becomes negative
D Becomes zero
In a purely resistive load, the current and voltage are in phase, meaning the power factor is 1. This indicates 100% efficiency with no reactive power and maximum transfer of real power.
What occurs during resonance in an RLC circuit?
A Voltage and current are out of phase
B Impedance increases
C Power factor decreases
D Current and voltage are in phase
At resonance in an RLC circuit, the inductive and capacitive reactances cancel each other out. As a result, the current and voltage become in phase, which means the power factor becomes 1, and maximum power is transferred.
What does reactive power represent in an AC circuit?
A Energy storage
B Energy loss
C Power consumed by resistive elements
D Power returned to the source
Reactive power represents energy that is alternately stored and released by inductive or capacitive components in an AC circuit. It does not perform any useful work but is necessary for creating magnetic and electric fields.
In a purely inductive circuit, what is the phase difference between voltage and current?
A 0 degrees
B 180 degrees
C 90 degrees
D 45 degrees
In a purely inductive circuit, the current lags the voltage by 90 degrees. This is due to the inductive reactance, where the inductor opposes changes in current, causing the current to shift behind the voltage waveform.
How is the total energy stored in a capacitor calculated?
A E = ½ LI²
B E = ½ CV²
C E = ½ RI²
D E = VI
The total energy stored in a capacitor is given by the formula E = ½ CV², where C is the capacitance and V is the voltage. This energy is stored in the electric field between the plates of the capacitor.
What effect does resonance have on the impedance of a series RLC circuit?
A No change
B Increases impedance
C Impedance becomes infinite
D Decreases impedance
At resonance, the impedance in a series RLC circuit is at its minimum. This is because the inductive reactance and capacitive reactance cancel each other out, leaving only the resistance to oppose the current.
What happens to the impedance in a parallel RLC circuit at resonance?
A Impedance becomes zero
B Impedance increases
C Impedance becomes infinite
D Impedance decreases
At resonance in a parallel RLC circuit, the impedance becomes infinite because the inductive and capacitive reactances cancel out. This results in no current flowing through the circuit, as the path is “open.”
What is the energy transfer rate in an AC circuit called?
A Power
B Voltage
C Impedance
D Resistance
The energy transfer rate in an AC circuit is called power. Power is the rate at which energy is used or generated in the circuit, and it is calculated by multiplying voltage, current, and the power factor.
How does energy storage in inductors affect AC circuits?
A Reduces voltage
B Opposes changes in current
C Opposes voltage
D Increases power factor
Inductors store energy in a magnetic field when current flows through them. They oppose changes in current by generating a back electromotive force (EMF), which resists any sudden increases or decreases in current flow.
What is the role of a power factor in reducing energy losses?
A Increases impedance
B Reduces current
C Decreases power
D Increases efficiency
A high power factor means that more of the power supplied to the circuit is being used effectively for useful work. Reducing reactive power (by improving power factor) helps decrease energy losses and improve efficiency in the system.