## Amateur Extra Class Exam Question Pool- Subelement E-5

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SUBELEMENT E5 - ELECTRICAL PRINCIPLES [4 Exam Questions - 4 Groups]

E5A -  Resonance and Q: characteristics of resonant circuits: series and parallel resonance; definitions and effects of Q; half-power bandwidth; phase relationships in reactive circuits

E5A01

What can cause the voltage across reactances in series to be larger than the voltage applied to them?

A. Resonance

B. Capacitance

C. Conductance

D. Resistance

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E5A02

What is resonance in an electrical circuit?

A. The highest frequency that will pass current

B. The lowest frequency that will pass current

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

D. The frequency at which the reactive impedance equals the resistive impedance

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E5A03

What is the magnitude of the impedance of a series RLC circuit at resonance?

A. High, as compared to the circuit resistance

B. Approximately equal to capacitive reactance

C. Approximately equal to inductive reactance

D. Approximately equal to circuit resistance

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E5A04

What is the magnitude of the impedance of a circuit with a resistor, an inductor and a capacitor all in parallel, at resonance?

A. Approximately equal to circuit resistance

B. Approximately equal to inductive reactance

C. Low, as compared to the circuit resistance

D. Approximately equal to capacitive reactance

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E5A05

What is the magnitude of the current at the input of a series RLC circuit as the frequency goes through resonance?

A. Minimum

B. Maximum

C. R/L

D. L/R

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E5A06

What is the magnitude of the circulating current within the components of a parallel LC circuit at resonance?

A. It is at a minimum

B. It is at a maximum

C. It equals 1 divided by the quantity 2 times Pi, multiplied by the square root of inductance L multiplied by capacitance C

D. It equals 2 multiplied by Pi, multiplied by frequency, multiplied by inductance

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E5A07

What is the magnitude of the current at the input of a parallel RLC circuit at resonance?

A. Minimum

B. Maximum

C. R/L

D. L/R

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E5A08

What is the phase relationship between the current through and the voltage across a series resonant circuit at resonance?

A. The voltage leads the current by 90 degrees

B. The current leads the voltage by 90 degrees

C. The voltage and current are in phase

D. The voltage and current are 180 degrees out of phase

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E5A09

How is the Q of an RLC parallel resonant circuit calculated?

A. Reactance of either the inductance or capacitance divided by the resistance

B. Reactance of either the inductance or capacitance multiplied by the resistance

C. Resistance divided by the reactance of either the inductance or capacitance

D. Reactance of the inductance multiplied by the reactance of the capacitance

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E5A10

How is the Q of an RLC series resonant circuit calculated?

A. Reactance of either the inductance or capacitance divided by the resistance

B. Reactance of either the inductance or capacitance times the resistance

C. Resistance divided by the reactance of either the inductance or capacitance

D. Reactance of the inductance times the reactance of the capacitance

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E5A11

What is the half-power bandwidth of a parallel resonant circuit that has a resonant frequency of 7.1 MHz and a Q of 150?

A. 157.8 Hz

B. 315.6 Hz

C. 47.3 kHz

D. 23.67 kHz

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E5A12

What is the half-power bandwidth of a parallel resonant circuit that has a resonant frequency of 3.7 MHz and a Q of 118?

A. 436.6 kHz

B. 218.3 kHz

C. 31.4 kHz

D. 15.7 kHz

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E5A13

What is an effect of increasing Q in a resonant circuit?

A. Fewer components are needed for the same performance

B. Parasitic effects are minimized

C. Internal voltages and circulating currents increase

D. Phase shift can become uncontrolled

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E5A14

What is the resonant frequency of a series RLC circuit if R is 22 ohms, L is 50 microhenrys and C is 40 picofarads?

A. 44.72 MHz

B. 22.36 MHz

C. 3.56 MHz

D. 1.78 MHz

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E5A15

Which of the following can increase Q for inductors and capacitors?

A. Lower losses

B. Lower reactance

C. Lower self-resonant frequency

D. Higher self-resonant frequency

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E5A16

What is the resonant frequency of a parallel RLC circuit if R is 33 ohms, L is 50 microhenrys and C is 10 picofarads?

A. 23.5 MHz

B. 23.5 kHz

C. 7.12 kHz

D. 7.12 MHz

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E5A17

What is the result of increasing the Q of an impedance-matching circuit?

A. Matching bandwidth is decreased

B. Matching bandwidth is increased

C. Matching range is increased

D. It has no effect on impedance matching

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E5B -  Time constants and phase relationships: RLC time constants; definition; time constants in RL and RC circuits; phase angle between voltage and current; phase angles of series RLC; phase angle of inductance vs susceptance; admittance and susceptance

E5B01

What is the term for the time required for the capacitor in an RC circuit to be charged to 63.2% of the applied voltage?

A. An exponential rate of one

B. One time constant

C. One exponential period

D. A time factor of one

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E5B02

What is the term for the time it takes for a charged capacitor in an RC circuit to discharge to 36.8% of its initial voltage?

A. One discharge period

B. An exponential discharge rate of one

C. A discharge factor of one

D. One time constant

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E5B03

What happens to the phase angle of a reactance when it is converted to a susceptance?

A. It is unchanged

B. The sign is reversed

C. It is shifted by 90 degrees

D. The susceptance phase angle is the inverse of the reactance phase angle

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E5B04

What is the time constant of a circuit having two 220 microfarad capacitors and two 1 megohm resistors, all in parallel?

A. 55 seconds

B. 110 seconds

C. 440 seconds

D. 220 seconds

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E5B05

What happens to the magnitude of a reactance when it is converted to a susceptance?

A. It is unchanged

B. The sign is reversed

C. It is shifted by 90 degrees

D. The magnitude of the susceptance is the reciprocal of the magnitude of the reactance

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E5B06

What is susceptance?

A. The magnetic impedance of a circuit

B. The ratio of magnetic field to electric field

C. The inverse of reactance

D. A measure of the efficiency of a transformer

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E5B07

What is the phase angle between the voltage across and the current through a series RLC circuit if XC is 500 ohms, R is 1 kilohm, and XL is 250 ohms?

A. 68.2 degrees with the voltage leading the current

B. 14.0 degrees with the voltage leading the current

C. 14.0 degrees with the voltage lagging the current

D. 68.2 degrees with the voltage lagging the current

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E5B08

What is the phase angle between the voltage across and the current through a series RLC circuit if XC is 100 ohms, R is 100 ohms, and XL is 75 ohms?

A. 14 degrees with the voltage lagging the current

B. 14 degrees with the voltage leading the current

C. 76 degrees with the voltage leading the current

D. 76 degrees with the voltage lagging the current

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E5B09

What is the relationship between the current through a capacitor and the voltage across a capacitor?

A. Voltage and current are in phase

B. Voltage and current are 180 degrees out of phase

C. Voltage leads current by 90 degrees

D. Current leads voltage by 90 degrees

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E5B10

What is the relationship between the current through an inductor and the voltage across an inductor?

A. Voltage leads current by 90 degrees

B. Current leads voltage by 90 degrees

C. Voltage and current are 180 degrees out of phase

D. Voltage and current are in phase

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E5B11

What is the phase angle between the voltage across and the current through a series RLC circuit if XC is 25 ohms, R is 100 ohms, and XL is 50 ohms?

A. 14 degrees with the voltage lagging the current

B. 14 degrees with the voltage leading the current

C. 76 degrees with the voltage lagging the current

D. 76 degrees with the voltage leading the current

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E5B12

A. The inverse of impedance

B. The term for the gain of a field effect transistor

C. The turns ratio of a transformer

D. The unit used for Q factor

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E5B13

What letter is commonly used to represent susceptance?

A. G

B. X

C. Y

D. B

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E5C -  Coordinate systems and phasors in electronics: Rectangular Coordinates; Polar Coordinates; Phasors

E5C01

Which of the following represents a capacitive reactance in rectangular notation?

A. –jX

B. +jX

C. X

D. Omega

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E5C02

How are impedances described in polar coordinates?

A. By X and R values

B. By real and imaginary parts

C. By phase angle and amplitude

D. By Y and G values

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E5C03

Which of the following represents an inductive reactance in polar coordinates?

A. A positive real part

B. A negative real part

C. A positive phase angle

D. A negative phase angle

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E5C04

Which of the following represents a capacitive reactance in polar coordinates?

A. A positive real part

B. A negative real part

C. A positive phase angle

D. A negative phase angle

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E5C05

What is the name of the diagram used to show the phase relationship between impedances at a given frequency?

A. Venn diagram

B. Near field diagram

C. Phasor diagram

D. Far field diagram

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E5C06

What does the impedance 50–j25 represent?

A. 50 ohms resistance in series with 25 ohms inductive reactance

B. 50 ohms resistance in series with 25 ohms capacitive reactance

C. 25 ohms resistance in series with 50 ohms inductive reactance

D. 25 ohms resistance in series with 50 ohms capacitive reactance

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E5C07

What is a vector?

A. The value of a quantity that changes over time

B. A quantity with both magnitude and an angular component

C. The inverse of the tangent function

D. The inverse of the sine function

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E5C08

What coordinate system is often used to display the phase angle of a circuit containing resistance, inductive and/or capacitive reactance?

C. Elliptical coordinates

D. Polar coordinates

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E5C09

When using rectangular coordinates to graph the impedance of a circuit, what does the horizontal axis represent?

A. Resistive component

B. Reactive component

C. The sum of the reactive and resistive components

D. The difference between the resistive and reactive components

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E5C10

When using rectangular coordinates to graph the impedance of a circuit, what does the vertical axis represent?

A. Resistive component

B. Reactive component

C. The sum of the reactive and resistive components

D. The difference between the resistive and reactive components

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E5C11

What do the two numbers that are used to define a point on a graph using rectangular coordinates represent?

A. The magnitude and phase of the point

B. The sine and cosine values

C. The coordinate values along the horizontal and vertical axes

D. The tangent and cotangent values

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E5C12

If you plot the impedance of a circuit using the rectangular coordinate system and find the impedance point falls on the right side of the graph on the horizontal axis, what do you know about the circuit?

A. It has to be a direct current circuit

B. It contains resistance and capacitive reactance

C. It contains resistance and inductive reactance

D. It is equivalent to a pure resistance

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E5C13

What coordinate system is often used to display the resistive, inductive, and/or capacitive reactance components of impedance?

C. Elliptical coordinates

D. Rectangular coordinates

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E5C14

Which point on Figure E5-2 best represents the impedance of a series circuit consisting of a 400 ohm resistor and a 38 picofarad capacitor at 14 MHz?

A. Point 2

B. Point 4

C. Point 5

D. Point 6

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E5C15

Which point in Figure E5-2 best represents the impedance of a series circuit consisting of a 300 ohm resistor and an 18 microhenry inductor at 3.505 MHz?

A. Point 1

B. Point 3

C. Point 7

D. Point 8

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E5C16

Which point on Figure E5-2 best represents the impedance of a series circuit consisting of a 300 ohm resistor and a 19 picofarad capacitor at 21.200 MHz?

A. Point 1

B. Point 3

C. Point 7

D. Point 8

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E5C17

Which point on Figure E5-2 best represents the impedance of a series circuit consisting of a 300 ohm resistor, a 0.64-microhenry inductor and an 85-picofarad capacitor at 24.900 MHz?

A. Point 1

B. Point 3

C. Point 5

D. Point 8

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E5D -  AC and RF energy in real circuits: skin effect; electrostatic and electromagnetic fields; reactive power; power factor; electrical length of conductors at UHF and microwave frequencies

E5D01

What is the result of skin effect?

A. As frequency increases, RF current flows in a thinner layer of the conductor, closer to the surface

B. As frequency decreases, RF current flows in a thinner layer of the conductor, closer to the surface

C. Thermal effects on the surface of the conductor increase the impedance

D. Thermal effects on the surface of the conductor decrease the impedance

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E5D02

Why is it important to keep lead lengths short for components used in circuits for VHF and above?

A. To increase the thermal time constant

B. To avoid unwanted inductive reactance

D. All of these choices are correct

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E5D03

What is microstrip?

A. Lightweight transmission line made of common zip cord

B. Miniature coax used for low power applications

C. Short lengths of coax mounted on printed circuit boards to minimize time delay between microwave circuits

D. Precision printed circuit conductors above a ground plane that provide constant impedance interconnects at microwave frequencies

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E5D04

Why are short connections necessary at microwave frequencies?

A. To increase neutralizing resistance

B. To reduce phase shift along the connection

C. Because of ground reflections

D. To reduce noise figure

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E5D05

Which parasitic characteristic increases with conductor length?

A. Inductance

B. Permeability

C. Permittivity

D. Malleability

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E5D06

In what direction is the magnetic field oriented about a conductor in relation to the direction of electron flow?

A. In the same direction as the current

B. In a direction opposite to the current

C. In all directions; omni-directional

D. In a direction determined by the left-hand rule

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E5D07

What determines the strength of the magnetic field around a conductor?

A. The resistance divided by the current

B. The ratio of the current to the resistance

C. The diameter of the conductor

D. The amount of current flowing through the conductor

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E5D08

What type of energy is stored in an electromagnetic or electrostatic field?

A. Electromechanical energy

B. Potential energy

C. Thermodynamic energy

D. Kinetic energy

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E5D09

What happens to reactive power in an AC circuit that has both ideal inductors and ideal capacitors?

A. It is dissipated as heat in the circuit

B. It is repeatedly exchanged between the associated magnetic and electric fields, but is not dissipated

C. It is dissipated as kinetic energy in the circuit

D. It is dissipated in the formation of inductive and capacitive fields

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E5D10

How can the true power be determined in an AC circuit where the voltage and current are out of phase?

A. By multiplying the apparent power times the power factor

B. By dividing the reactive power by the power factor

C. By dividing the apparent power by the power factor

D. By multiplying the reactive power times the power factor

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E5D11

What is the power factor of an R-L circuit having a 60 degree phase angle between the voltage and the current?

A. 1.414

B. 0.866

C. 0.5

D. 1.73

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E5D12

How many watts are consumed in a circuit having a power factor of 0.2 if the input is 100-VAC at 4 amperes?

A. 400 watts

B. 80 watts

C. 2000 watts

D. 50 watts

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E5D13

How much power is consumed in a circuit consisting of a 100 ohm resistor in series with a 100 ohm inductive reactance drawing 1 ampere?

A. 70.7 Watts

B. 100 Watts

C. 141.4 Watts

D. 200 Watts

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E5D14

What is reactive power?

A. Wattless, nonproductive power

B. Power consumed in wire resistance in an inductor

C. Power lost because of capacitor leakage

D. Power consumed in circuit Q

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E5D15

What is the power factor of an R-L circuit having a 45 degree phase angle between the voltage and the current?

A. 0.866

B. 1.0

C. 0.5

D. 0.707

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E5D16

What is the power factor of an R-L circuit having a 30 degree phase angle between the voltage and the current?

A. 1.73

B. 0.5

C. 0.866

D. 0.577

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E5D17

How many watts are consumed in a circuit having a power factor of 0.6 if the input is 200VAC at 5 amperes?

A. 200 watts

B. 1000 watts

C. 1600 watts

D. 600 watts

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E5D18

How many watts are consumed in a circuit having a power factor of 0.71 if the apparent power is 500VA?

A. 704 W

B. 355 W

C. 252 W

D. 1.42 mW

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