Resonance in an RLC circuit occurs when the inductive reactance and capacitive reactance cancel each other out. This results in the total impedance being at a minimum, allowing maximum current to flow through the circuit.
What is the phase relationship between current and voltage in a purely inductive AC circuit?
A Zero voltage
B In phase
C 180° out of phase
D 90° out of phase
In a purely inductive AC circuit, the current lags the voltage by 90°. This means that the peak current occurs a quarter of a cycle after the peak voltage, causing a phase shift of 90°.
How does an increase in frequency affect the impedance of an inductor?
A Becomes constant
B No effect
C Increases
D Decreases
The impedance of an inductor increases with frequency because inductive reactance is directly proportional to the frequency of the AC signal. Higher frequencies result in greater opposition to current flow through the inductor.
What does a power factor of 1 indicate in an AC circuit?
A Zero voltage
B Maximum efficiency
C High power loss
D Low current
A power factor of 1 indicates perfect efficiency in an AC circuit, where all the supplied power is being used effectively. It means the voltage and current are in phase, resulting in no reactive power.
What happens to the current in a series RLC circuit at resonance?
A Increases
B Remains constant
C Decreases
D Becomes zero
At resonance in a series RLC circuit, the impedance is minimized, which allows maximum current to flow through the circuit. The resonant frequency occurs when the inductive and capacitive reactances cancel each other out.
What is the effect of adding more resistors in parallel to a circuit?
A Increases current flow
B Increases total resistance
C No effect
D Decreases total resistance
In a parallel circuit, the total resistance decreases as more resistors are added. This is because the reciprocal of the total resistance is the sum of the reciprocals of individual resistances.
What does an impedance of zero indicate in an AC circuit?
A Infinite power
B Open circuit
C Short circuit
D Maximum current
An impedance of zero in an AC circuit indicates a short circuit, where the current can flow without opposition. This condition occurs when there is a direct path with no resistance or reactance.
What type of power is dissipated in the form of heat in an AC circuit?
A Apparent power
B Real power
C Total power
D Reactive power
Real power (measured in watts) is the power that is actually consumed or dissipated as heat in resistive components of an AC circuit. It represents the useful power available to do work.
What is the formula for calculating impedance in a series RLC circuit?
A Z = R – Xₗ
B Z = R + Xₗ
C Z = √(R² + Xₗ²)
D Z = √(R + Xₗ)
In a series RLC circuit, the total impedance (Z) is calculated by taking the square root of the sum of the squares of the resistance (R) and the inductive reactance (Xₗ). This gives the overall opposition to current.
What does a low power factor signify in an AC circuit?
A Poor efficiency
B Low voltage
C High impedance
D High current
A low power factor indicates poor efficiency, meaning that a large portion of the supplied power is being wasted as reactive power. It usually happens when voltage and current are not in phase.
What is the main purpose of using a capacitor in an AC circuit?
A Decrease impedance
B Increase current
C Reduce power loss
D Store electrical energy
A capacitor stores electrical energy in the form of an electric field between its plates. In an AC circuit, it temporarily stores energy and then releases it, helping smooth out fluctuations in voltage.
What happens when the power factor is less than 1?
A No power is transmitted
B Part of the power is wasted
C Maximum power usage
D Voltage leads current
When the power factor is less than 1, part of the power is wasted as reactive power. This means that not all the power is being used effectively for work, leading to inefficiency in the system.
What is true about impedance in a purely capacitive AC circuit?
A Impedance is negative
B High impedance
C Impedance equals reactance
D Zero impedance
In a purely capacitive AC circuit, the impedance is equal to the capacitive reactance. The impedance opposes the flow of alternating current and is inversely proportional to the frequency of the signal.
What happens when the frequency of an AC signal increases in a parallel RLC circuit?
A Impedance decreases
B Current decreases
C Impedance increases
D Current increases
In a parallel RLC circuit, as the frequency increases, the impedance typically decreases. At resonance, the impedance is at its minimum, allowing maximum current to flow through the circuit.
What is the result of resonance in a series RLC circuit?
A Zero voltage
B Maximum impedance
C Maximum current
D Minimum current
In a series RLC circuit, resonance occurs when the inductive and capacitive reactances cancel each other out. This results in the lowest impedance and allows maximum current to flow through the circuit at the resonant frequency.