Introduction to AC Circuits: Master the Fundamentals of Alternating Current

Question 1

In an AC circuit, what condition defines resonance and what are its practical implications?

Accepted Answer

Resonance occurs when the inductive reactance (XL) equals the capacitive reactance (XC), resulting in maximum current flow.

Answer

Resonance happens when the circuit's resistance becomes zero, leading to a short circuit.

Answer

Resonance is a phenomenon exclusive to DC circuits, where voltage and current are constant.

Answer

Resonance has no practical applications in electrical engineering.

Question 2

In AC circuits, how does impedance differ from resistance?

Accepted Answer

Impedance is a complex quantity with magnitude and phase angle, while resistance is a scalar quantity.

Answer

Impedance is the same as resistance, regardless of the AC signal's frequency.

Answer

Impedance is only found in AC circuits, while resistance is found in both AC and DC circuits.

Question 3

In an AC circuit, what is the phase relationship between voltage (V) and current (I) in a pure resistor?

Accepted Answer

V and I are in phase

Answer

V lags I by 90°

Answer

V leads I by 90°

Answer

V and I are anti-phase

Question 4

In an RL circuit, what happens to the current when the inductive reactance is increased?

Accepted Answer

Current decreases

Answer

Current increases

Answer

Current remains the same

Answer

Current becomes negative

Question 5

Which of the following components is NOT a passive element in an AC circuit?

Accepted Answer

Voltage source

Answer

Resistor

Answer

Capacitor

Answer

Inductor

Question 6

In a series AC circuit, what happens to the voltage across a capacitor when the frequency of the AC source increases?

Accepted Answer

Voltage across capacitor increases

Answer

Voltage across capacitor decreases

Answer

Voltage across capacitor remains the same

Answer

Voltage across capacitor becomes zero

Question 7

Which of the following correctly describes the direction of current flow in an alternating current (AC) circuit?

Accepted Answer

It periodically reverses direction.

Answer

It flows in one fixed direction.

Answer

It flows randomly in both directions.

Answer

It has a constant direction but varies in magnitude.

Question 8

In a purely resistive AC circuit, the relationship between voltage and current is:

Accepted Answer

In phase

Answer

90° out of phase

Answer

180° out of phase

Answer

Phase relationship depends on circuit parameters

Question 9

In an AC circuit containing an inductor, energy is stored in the form of:

Accepted Answer

Magnetic field

Answer

Electric field

Answer

Thermal energy

Answer

Kinetic energy

Question 10

Which factor does NOT affect the value of the resonant frequency in a series LC circuit?

Accepted Answer

Voltage

Answer

Inductance

Answer

Capacitance

Answer

Resistance

Question 11

In an AC circuit, the power factor is unity when:

Accepted Answer

Voltage and current are in phase

Answer

Voltage and current are 90° out of phase

Answer

Voltage and current are 180° out of phase

Answer

Voltage and current are randomly out of phase

Question 12

Which type of AC power transformer is used to provide electrical isolation between two circuits while maintaining voltage levels?

Accepted Answer

Isolation transformer

Answer

Step-up transformer

Answer

Step-down transformer

Answer

Autotransformer

Question 13

In an AC circuit, which component typically exhibits the highest impedance?

Accepted Answer

Inductor

Answer

Resistor

Answer

Capacitor

Answer

Diode

Question 14

What is the primary function of a rectifier in an AC circuit?

Accepted Answer

To convert AC to DC

Answer

To regulate voltage

Answer

To smooth out waveforms

Answer

To amplify signals

Question 15

In power systems, what is the main purpose of transformers?

Accepted Answer

Regulating voltage levels

Answer

Correcting power factor

Answer

Eliminating harmonics

Answer

Converting alternating current (AC) to direct current (DC)

Question 16

In AC circuits, during which interval is the sinusoidal waveform repeated regularly?

Accepted Answer

Period

Answer

Frequency

Answer

Wavelength

Answer

Amplitude

Question 17

Which characteristic does NOT apply to an inductor in an AC circuit?

Accepted Answer

Allows current to flow freely without opposition

Answer

Opposes changes in current flow

Answer

Induces a phase shift in current

Answer

Stores energy in its magnetic field

Question 18

In a series RLC circuit, what condition must be met for maximum power transfer?

Accepted Answer

Inductive reactance (XL) equals capacitive reactance (XC)

Answer

XL is less than XC

Answer

Resistance (R) is zero

Answer

XL is greater than XC

Question 19

What is a major disadvantage associated with AC transmission compared to DC transmission?

Accepted Answer

Higher transmission losses due to inductive and capacitive effects

Answer

Necessity for more conductive wires

Answer

Requirement for more complex equipment

Answer

Lower overall efficiency

Question 20

What is the primary purpose of using a transformer in an AC circuit?

Accepted Answer

To change voltage and/or current levels

Answer

To block direct current (DC) components

Answer

To protect the circuit from overloads

Answer

To improve power factor

Question 21

Which mathematical expression represents the impedance (Z) of an AC circuit?

Accepted Answer

Z = R + j(XL - XC)

Answer

Z = R^2 + (XL - XC)^2

Question 22

Which formula accurately represents the inductive reactance (XL) of an inductor in an AC circuit?

Accepted Answer

XL = 2πfL

Answer

XL = L/2πf

Answer

XL = fL

Answer

XL = f/2πL

Question 23

What is the definition of power factor in an AC circuit?

Accepted Answer

The ratio of true power to apparent power

Answer

The ratio of apparent power to true power

Answer

The ratio of reactive power to true power

Answer

The ratio of true power to reactive power

Question 24

In an AC circuit, a capacitor stores energy in what form?

Accepted Answer

An electric field

Answer

Potential energy

Answer

Kinetic energy

Answer

A magnetic field

Question 25

In an AC circuit, the current through a resistor is in phase with which of the following?

Accepted Answer

The applied voltage

Answer

The current through a capacitor

Answer

The current through an inductor

Answer

The power in the circuit

Question 26

What does the impedance of an AC circuit represent?

Accepted Answer

The total opposition to current flow, expressed as a complex number

Answer

The resistance of the circuit

Answer

The reactance of the circuit

Question 27

What does the quality factor (Q) of an inductor measure?

Accepted Answer

Its energy storage capability relative to its energy dissipation

Answer

Its capacitance relative to its resistance

Answer

Its inductance relative to its resistance

Question 28

What is the term for the frequency at which an AC circuit exhibits maximum power transfer?

Accepted Answer

Resonant frequency

Answer

Natural frequency

Answer

Cut-off frequency

Answer

Critical frequency

Question 29

In a purely capacitive AC circuit, what is the phase relationship between the voltage across the capacitor and the current through it?

Accepted Answer

Current leads voltage by 90 degrees.

Answer

Voltage and current are 180 degrees out of phase.

Answer

Voltage leads current by 90 degrees.

Answer

Voltage and current are in phase.

Question 30

Consider a series RLC circuit with a resistance of 10Ω, an inductive reactance of 20Ω, and a capacitive reactance of 10Ω. Calculate the circuit's impedance.

Accepted Answer

22.4Ω

Answer

20Ω

Answer

40Ω

Answer

10Ω

Question 31

In a series AC circuit, what mathematical operation is used to combine the individual component voltages to obtain the total applied voltage?

Accepted Answer

phasor sum

Answer

difference

Answer

arithmetic sum

Answer

product

Question 32

In a purely inductive AC circuit, what is the average power dissipated over a complete cycle?

Accepted Answer

0W

Answer

Equal to the reactive power

Answer

Maximum at all times

Question 33

What does the power factor of an AC circuit indicate?

Accepted Answer

The efficiency of the circuit in converting electrical energy to work

Answer

The circuit's total opposition to current flow

Answer

The energy stored in the circuit's reactive elements

Question 34

Which unit is used to express the capacitive reactance of a component?

Accepted Answer

ohm

Answer

farad

Answer

watt

Answer

henry

Question 35

A sinusoidal voltage waveform has a peak value of 100 volts. What is its RMS (root-mean-square) value?

Accepted Answer

70.7 volts

Answer

50 volts

Answer

100 volts

Question 36

An inductor is connected to an AC source. What is the phase relationship between the current and voltage in this circuit?

Accepted Answer

The current lags the voltage by 90 degrees.

Answer

The current and voltage are in phase.

Answer

The current leads the voltage by 90 degrees.

Question 37

What is the unit of measurement for capacitive reactance?

Accepted Answer

Ohms

Answer

Siemens

Answer

Henries

Answer

Farads

Question 38

An AC circuit contains a resistor, a capacitor, and an inductor connected in series. What is the term used to describe the combined effect of these components on the circuit's current and voltage?

Accepted Answer

Impedance

Answer

Reactance

Answer

Resistance

Answer

Susceptance

Question 39

The power factor of an AC circuit is a measure of:

Accepted Answer

The phase difference between voltage and current.

Answer

The amount of power dissipated in the circuit.

Answer

The efficiency of the circuit.

Answer

The total resistance in the circuit.

Question 40

A series RLC circuit is connected to an AC source. What condition must be met for resonance to occur in this circuit?

Accepted Answer

The capacitive reactance equals the inductive reactance.

Answer

The current is maximum.

Answer

The impedance is zero.

Question 41

In an AC circuit, the current and voltage are represented by the functions i(t) = I_m sin(ωt) and v(t) = V_m sin(ωt + φ), respectively. What is the phase difference between the current and voltage?

Accepted Answer

φ

Answer

0

Answer

π

Answer

π/2

Question 42

Which of the following statements is true for a resistor in an AC circuit?

Accepted Answer

The current and voltage are in phase.

Answer

The current leads the voltage by π/2.

Answer

The current and voltage are out of phase by π.

Answer

The voltage leads the current by π/2.

Question 43

In an AC circuit, the impedance of an inductor is given by:

Accepted Answer

jωL

Answer

1/jωL

Answer

R + jωL

Answer

-jωL

Question 44

Which of the following is a property of a capacitor in an AC circuit?

Accepted Answer

It stores energy in its electric field.

Answer

It has no effect on AC current.

Answer

It dissipates energy as heat.

Answer

It blocks DC current.

Question 45

In an AC circuit, the power factor is:

Accepted Answer

The ratio of real power to apparent power.

Answer

The ratio of reactive power to apparent power.

Answer

The ratio of apparent power to reactive power.

Answer

The ratio of real power to reactive power.

Question 46

Which of the following is a benefit of using AC over DC in power transmission?

Accepted Answer

Reduced power loss due to lower resistance.

Answer

Easier conversion to different voltage levels.

Answer

Less susceptibility to electromagnetic interference.

Answer

Increased safety due to lower voltage.

Question 47

What is the resonant frequency of an AC circuit?

Accepted Answer

The frequency at which the inductive reactance equals the capacitive reactance.

Answer

The frequency at which the voltage is maximum.

Answer

The frequency at which the current is maximum.

Question 48

What is the skin effect in AC circuits?

Accepted Answer

The tendency of current to flow near the surface of a conductor.

Answer

The tendency of current to flow through the center of a conductor.

Answer

The tendency of voltage to drop across a conductor.

Question 49

Which of the following is a way to reduce the skin effect in AC circuits?

Accepted Answer

Using stranded conductors.

Answer

Using shorter conductors.

Answer

Using larger conductors.

Question 50

A sinusoidal voltage waveform has a peak value of 100V. What is its RMS value?

Accepted Answer

70.7V

Answer

100V

Answer

50V

Answer

141.4V

Question 51

Which of the following components exhibits a 90-degree phase shift between voltage and current in an AC circuit?

Accepted Answer

Capacitor

Answer

Inductor

Answer

Resistor

Question 52

What is the impedance of a 100Ω resistor in an AC circuit with a frequency of 60Hz?

Accepted Answer

100Ω

Answer

0Ω

Answer

60Ω

Answer

Infinity

Question 53

A capacitor with a capacitance of 10μF is connected to a 120V, 60Hz AC source. What is the capacitive reactance?

Accepted Answer

265.26Ω

Answer

60Ω

Answer

120Ω

Answer

10Ω

Question 54

An inductor with an inductance of 2H is connected to a 240V, 50Hz AC source. What is the inductive reactance?

Accepted Answer

628.32Ω

Answer

240Ω

Answer

50Ω

Question 55

An AC circuit consists of a 100Ω resistor, a 10μF capacitor, and a 2H inductor connected in series. What is the total impedance of the circuit at a frequency of 50Hz?

Accepted Answer

141.42Ω

Answer

100Ω

Answer

200Ω

Answer

316.23Ω

Question 56

In an RLC series circuit, the current leads the voltage when the circuit is:

Accepted Answer

Capacitive

Answer

Resistive

Answer

Resonant

Answer

Inductive

Question 57

What is the power factor of a circuit with an impedance of 10Ω and a resistance of 8Ω?

Accepted Answer

0.8

Answer

0.5

Answer

0.2

Answer

1

Question 58

The phenomenon where the impedance of an RLC series circuit becomes minimum is called:

Accepted Answer

Resonance

Answer

Impedance matching

Answer

Inductance

Answer

Capacitance

Question 59

Which of the following statements is TRUE about the average power consumed by a pure inductor in an AC circuit?

Accepted Answer

Zero

Answer

Depends on the frequency

Answer

Maximum

Answer

Half of the peak power