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M3 > 3.14 RLC Circuits > Flashcards

3.14 RLC Circuits Flashcards

1
Q
A
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2
Q

What is the difference between resistance and reactance in electrical circuits?

A

Resistance dissipates energy as heat, while reactance stores energy and returns it to the circuit

Reactance is measured in ohms but is not the same as resistance.

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3
Q

What are the two types of reactance?

A
  • Capacitive reactance
  • Inductive reactance
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4
Q

How do AC voltage and current behave in circuits with reactance?

A

They are out of phase with each other.

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5
Q

What does LCR stand for in electrical circuits?

A

Inductors, Capacitors, and Resistors.

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6
Q

True or False: In a DC circuit, both AC and DC light bulbs glow with the same brightness.

A

True

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7
Q

What is a ‘real load’ in electrical circuits?

A

A load that produces a measurable effect, converting electrical energy into another form of energy.

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8
Q

What is the phase relationship between current and voltage in a real load?

A

Current and voltage are in phase.

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9
Q

In an AC circuit, how can resistance be calculated?

A

Using the RMS values of voltage and current by applying Ohm’s law.

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10
Q

What is the effect of inductive reactance on AC current?

A

It causes the AC current to be smaller than the DC current.

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11
Q

What causes the phase shift in a purely inductive circuit?

A

The self-induced voltage opposes the applied voltage.

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12
Q

What is the phase angle between current and voltage in a purely inductive circuit?

A

90° or π/2 radians.

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13
Q

What is a phasor diagram?

A

An alternative way of representing sinusoidal variables using vectors that rotate at a steady angular speed.

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14
Q

How is inductive reactance affected by frequency?

A

It increases with higher frequency.

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15
Q

What happens to AC current in a capacitor compared to a DC circuit?

A

In a DC circuit, no current flows after initial charging, while in an AC circuit, the current repeatedly rises and falls.

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16
Q

What is capacitive reactance?

A

The opposition a capacitor presents to the flow of AC current.

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17
Q

How does the phase relationship between current and voltage behave in a circuit with only capacitive reactance?

A

The current leads the applied voltage by 90°.

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18
Q

What happens at the peak values of voltage in a capacitive circuit?

A

Voltage is at its peak value when current is zero.

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19
Q

What is the formula for calculating capacitive reactance?

A

Capacitive reactance = 1 / (2πfC)

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20
Q

What is the effect of increasing capacitance on capacitive reactance?

A

It decreases capacitive reactance.

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21
Q

How does frequency affect capacitive reactance?

A

It decreases as frequency increases.

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22
Q

What are the two types of reactance in AC circuits?

A

Capacitive reactance and inductive reactance

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23
Q

What is reactive energy?

A

Energy stored in the electric field of a capacitor or in the magnetic field of an inductor during a cycle of AC

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24
Q

What is the formula for true power in AC circuits?

A

P = V * I

Where P is power in watts (W), V is voltage in volts (V), and I is resistive current in amps (A)

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25
Q

What is true power also known as?

A

Real power or effective power

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26
Q

What is the unit for true power?

A

Watt (W)

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27
Q

In a pure inductor, how does the current relate to the voltage?

A

Current lags the voltage by 90°

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28
Q

What does positive power represent in a purely inductive load?

A

Power supplied to the inductor by the circuit

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29
Q

What is inductive reactive power?

A

Power that is not dissipated as heat, light, or mechanical energy in a purely inductive load

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30
Q

What is the symbol for inductive reactive power?

A

Q_L

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31
Q

What is the unit for inductive reactive power?

A

Volt-ampere reactive (VAr)

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32
Q

In a purely capacitive load, how does the current relate to the voltage?

A

Current leads the voltage by 90°

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33
Q

What is capacitive reactive power?

A

Power that is not dissipated as heat, light, or mechanical energy in a purely capacitive load

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34
Q

What is the symbol for capacitive reactive power?

A

Q_C

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35
Q

What is the unit for capacitive reactive power?

A

Volt-ampere reactive (VAr)

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36
Q

How can a real coil be represented for analysis?

A

As a pure inductor in series with a pure resistor

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37
Q

What is apparent power?

A

The product of RMS voltage and RMS current measured in an AC circuit

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38
Q

What is the formula for apparent power?

A

S = V * I

Where S is apparent power in volt-ampere (VA), V is RMS voltage in volts (V), and I is RMS current in amps (A)

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39
Q

What is the unit for apparent power?

A

Volt-ampere (VA)

40
Q

True or False: The true power is always greater than the apparent power.

A

False

41
Q

What is the opposition to current flow in a purely resistive circuit called?

A

Resistance R

42
Q

In an AC circuit, what is the term used for the opposition to current flow caused by inductors and capacitors?

A

Reactance

43
Q

What symbols represent inductive and capacitive reactance?

A

Inductive reactance: XL, Capacitive reactance: XC

44
Q

What is the overall measure of opposition to AC in a circuit called?

A

Impedance Z

45
Q

How is impedance Z calculated in relation to resistance R and reactance?

A

Vector addition (geometric addition) must be used

46
Q

What theorem is applied to determine unknown values of power or current in AC circuits?

A

Pythagoras’s theorem

47
Q

What is the relationship between inductive reactance and frequency?

A

Inductive reactance is directly proportional to frequency

48
Q

What happens to capacitive reactance as frequency increases?

A

Capacitive reactance decreases

49
Q

What effect does high frequency have on the resistance of a conductor?

A

Resistance can increase due to the skin effect

50
Q

What is the effective resistance range below which it is considered constant?

A

0 Hz to approximately 1000 Hz

51
Q

What is the formula that relates RMS voltage, RMS current, and impedance in AC circuits?

A

Z = V / I

52
Q

In a series connection of a resistor and inductor, how does the current relate to the voltage across the resistor?

A

The voltage VR is in phase with the current I

53
Q

In a coil, how does the current relate to the voltage across the inductive reactance?

A

The current I lags the voltage VL by 90°

54
Q

What is the shape of the triangle formed in the phasor diagram for a series connection of resistance and inductance?

A

Right-angled triangle

55
Q

What is the phase relationship between the voltage phasor VL and the current phasor I?

A

Voltage phasor VL is perpendicular to current phasor I

56
Q

What geometric method is used to determine the resultant voltage across a coil?

A

Geometric addition of the phasors VR and VL

57
Q

In a series connection of a resistor and capacitor, how does the current relate to the voltage across the resistor?

A

The voltage VR is in phase with the current I

58
Q

How does the current relate to the voltage across the capacitive reactance in a series connection?

A

The current I leads the voltage VC by 90°

59
Q

What is the term for the resistance present in real capacitors?

A

Loss resistance

60
Q

What is the phase angle between the total current I and the applied voltage V in a parallel circuit?

A

Between 0° and 90°

61
Q

What is the formula for calculating total current in a parallel resistor and capacitor circuit?

A

I = IR + IC

62
Q

What happens to the phase angle in real capacitors due to loss resistance?

A

The phase angle is always less than 90°

63
Q

In a series connection of a resistor, coil, and capacitor, what must be performed to find the total voltage?

A

Geometric addition of the voltages across VR, VL, and VC

64
Q

What is the relationship between the voltages VL and VC in a series connection?

A

They act in opposite directions and can be subtracted from one another

65
Q

What is the relationship between voltage and current in a coil?

A

For the coil, the voltage leads the current

This indicates that the voltage reaches its maximum value before the current does.

66
Q

What is the relationship between voltage and current in a capacitor?

A

For the capacitor, the voltage lags the current

This means that the current reaches its maximum value before the voltage does.

67
Q

In a series circuit with a resistor, coil, and capacitor, what is the phase angle between the voltage phasors VL and VC?

A

180°

This indicates that VL and VC act in opposite directions.

68
Q

How is the supplied RMS voltage calculated in a series circuit with L, C, and R?

A

It is equal to the geometric sum of phasors for the three component voltages.

69
Q

What theorem is applied to calculate unknown values in LCR series circuits?

A

Pythagoras’s theorem

70
Q

What are the three types of reactance in LCR circuits?

A
  • Capacitive reactance (XC)
  • Inductive reactance (XL)
  • Resistance (R)
71
Q

When inductive reactance XL is greater than capacitive reactance XC, how is the circuit characterized?

A

The circuit is mainly inductive.

72
Q

When capacitive reactance XC is greater than inductive reactance XL, how is the circuit characterized?

A

The circuit is mainly capacitive.

73
Q

What occurs when inductive reactance XL and capacitive reactance XC are equal?

A

The circuit operates like a purely resistive load.

74
Q

In a parallel circuit with a resistor, inductor, and capacitor, what is the common factor?

A

The applied RMS voltage V

75
Q

What happens to the supplied current I in a parallel circuit with L, C, and R?

A

It is equal to the geometric sum of the three current phasors.

76
Q

What is the phase relationship between the current phasors IL and IC in a parallel circuit?

A

They have a phase angle of 180°.

77
Q

What happens if the current through the inductive reactance is higher than that through the capacitive reactance?

A

The circuit is inductive.

78
Q

What happens if the current through the capacitive reactance is higher than that through the inductive reactance?

A

The circuit is capacitive.

79
Q

What does the power factor indicate?

A

The fraction of apparent power S that is converted into true power P.

80
Q

What is the ideal value for the power factor to maximize true power?

A

As close to 1 as possible.

81
Q

Fill in the blank: The power factor is affected by the presence of _______ in a device or circuit.

A

inductive reactance

82
Q

What does a power factor of less than 1 typically indicate?

A

The presence of reactive power in the circuit.

83
Q

What is real power?

A

Real power is transferred to the environment by the circuit or device.

84
Q

What is reactive power?

A

Reactive power is stored and returned to the circuit later in the AC cycle.

85
Q

Why is reactive power important in AC circuits?

A

It increases the supply voltage and power, making it an important consideration in design, operation, and maintenance.

86
Q

How must power be treated when designing AC electrical systems?

A

Power must be treated as a vector quantity.

87
Q

What mathematical theorem is applied in power calculations for AC systems?

A

Pythagoras’s theorem.

88
Q

What is the relationship between voltage, current, and power in AC circuits?

A

One can multiply each voltage by the current to determine the power associated with each.

89
Q

What is the formula for apparent power?

A

Apparent power is the result of the geometric addition of true and reactive power.

90
Q

What units are used to rate AC generators and transformers?

A

Volt-Ampere (VA).

91
Q

What units are used to indicate the mechanical output power of engines?

A

Watts (W).

92
Q

Fill in the blank: Apparent power is the result of the geometric addition of _______ and _______.

A

true power, reactive power.

93
Q

True or False: True power is always equal to apparent power in AC circuits.

A

False.

94
Q

What do the information plates of engines indicate?

A

The mechanical output power delivered to the shaft in units of Watts.

95
Q

What must electrical systems and transmission lines be designed for?

A

Apparent power.

96
Q

What is the main consideration when analyzing voltages across inductance and resistance in series?

A

Vector analysis.

97
Q

What type of functions can be applied to calculate power in AC systems?

A

Trigonometric functions.

M3 (19 decks)

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