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effective 7/01/2016 thru 6/29/2020

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Topic 2016-E5: Electrical Principles


2016-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

2016-E5A01: What can cause the voltage across reactances in series to be larger than the voltage applied to them?

Resonance

Capacitance

Conductance

Resistance



2016-E5A02: What is resonance in an electrical circuit?

The frequency at which the capacitive reactance equals the inductive reactance

The highest frequency that will pass current

The lowest frequency that will pass current

The frequency at which the reactive impedance equals the resistive impedance



2016-E5A03: What is the magnitude of the impedance of a series RLC circuit at resonance?

Approximately equal to circuit resistance

High, as compared to the circuit resistance

Approximately equal to capacitive reactance

Approximately equal to inductive reactance



2016-E5A04: What is the magnitude of the impedance of a circuit with a resistor, an inductor and a capacitor all in parallel, at resonance?

Approximately equal to circuit resistance

Approximately equal to inductive reactance

Low, as compared to the circuit resistance

Approximately equal to capacitive reactance



2016-E5A05: What is the magnitude of the current at the input of a series RLC circuit as the frequency goes through resonance?

Maximum

Minimum

R/L

L/R



2016-E5A06: What is the magnitude of the circulating current within the components of a parallel LC circuit at resonance?

It is at a maximum

It is at a minimum

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

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



2016-E5A07: What is the magnitude of the current at the input of a parallel RLC circuit at resonance?

Minimum

Maximum

R/L

L/R



2016-E5A08: What is the phase relationship between the current through and the voltage across a series resonant circuit at resonance?

The voltage and current are in phase

The voltage leads the current by 90 degrees

The current leads the voltage by 90 degrees

The voltage and current are 180 degrees out of phase



2016-E5A09: How is the Q of an RLC parallel resonant circuit calculated?

Resistance divided by the reactance of either the inductance or capacitance

Reactance of either the inductance or capacitance divided by the resistance

Reactance of either the inductance or capacitance multiplied by the resistance

Reactance of the inductance multiplied by the reactance of the capacitance



2016-E5A10: How is the Q of an RLC series resonant circuit calculated?

Reactance of either the inductance or capacitance divided by the resistance

Reactance of either the inductance or capacitance times the resistance

Resistance divided by the reactance of either the inductance or capacitance

Reactance of the inductance times the reactance of the capacitance



2016-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?

47.3 kHz

157.8 Hz

315.6 Hz

23.67 kHz



2016-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?

31.4 kHz

436.6 kHz

218.3 kHz

15.7 kHz



2016-E5A13: What is an effect of increasing Q in a resonant circuit?

Internal voltages and circulating currents increase

Fewer components are needed for the same performance

Parasitic effects are minimized

Phase shift can become uncontrolled



2016-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?

3.56 MHz

44.72 MHz

22.36 MHz

1.78 MHz



2016-E5A15: Which of the following can increase Q for inductors and capacitors?

Lower losses

Lower reactance

Lower self-resonant frequency

Higher self-resonant frequency



2016-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?

7.12 MHz

23.5 MHz

23.5 kHz

7.12 kHz



2016-E5A17: What is the result of increasing the Q of an impedance-matching circuit?

Matching bandwidth is decreased

Matching bandwidth is increased

Matching range is increased

It has no effect on impedance matching






2016-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

2016-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?

One time constant

An exponential rate of one

One exponential period

A time factor of one



2016-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?

One time constant

One discharge period

An exponential discharge rate of one

A discharge factor of one



2016-E5B03: What happens to the phase angle of a reactance when it is converted to a susceptance?

The sign is reversed

It is unchanged

It is shifted by 90 degrees

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



2016-E5B04: What is the time constant of a circuit having two 220 microfarad capacitors and two 1 megohm resistors, all in parallel?

220 seconds

55 seconds

110 seconds

440 seconds



2016-E5B05: What happens to the magnitude of a reactance when it is converted to a susceptance?

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

It is unchanged

The sign is reversed

It is shifted by 90 degrees



2016-E5B06: What is susceptance?

The inverse of reactance

The magnetic impedance of a circuit

The ratio of magnetic field to electric field

A measure of the efficiency of a transformer



2016-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?

14.0 degrees with the voltage lagging the current

68.2 degrees with the voltage leading the current

14.0 degrees with the voltage leading the current

68.2 degrees with the voltage lagging the current



2016-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?

14 degrees with the voltage lagging the current

14 degrees with the voltage leading the current

76 degrees with the voltage leading the current

76 degrees with the voltage lagging the current



2016-E5B09: What is the relationship between the current through a capacitor and the voltage across a capacitor?

Current leads voltage by 90 degrees

Voltage and current are in phase

Voltage and current are 180 degrees out of phase

Voltage leads current by 90 degrees



2016-E5B10: What is the relationship between the current through an inductor and the voltage across an inductor?

Voltage leads current by 90 degrees

Current leads voltage by 90 degrees

Voltage and current are 180 degrees out of phase

Voltage and current are in phase



2016-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?

14 degrees with the voltage leading the current

14 degrees with the voltage lagging the current

76 degrees with the voltage lagging the current

76 degrees with the voltage leading the current



2016-E5B12: What is admittance?

The inverse of impedance

The term for the gain of a field effect transistor

The turns ratio of a transformer

The unit used for Q factor



2016-E5B13: What letter is commonly used to represent susceptance?

B

G

X

Y






2016-E5C: Coordinate systems and phasors in electronics: Rectangular Coordinates; Polar Coordinates; Phasors

2016-E5C01: Which of the following represents a capacitive reactance in rectangular notation?

-jX

+jX

X

Omega



2016-E5C02: How are impedances described in polar coordinates?

By phase angle and amplitude

By X and R values

By real and imaginary parts

By Y and G values



2016-E5C03: Which of the following represents an inductive reactance in polar coordinates?

A positive phase angle

A positive real part

A negative real part

A negative phase angle



2016-E5C04: Which of the following represents a capacitive reactance in polar coordinates?

A negative phase angle

A positive real part

A negative real part

A positive phase angle



2016-E5C05: What is the name of the diagram used to show the phase relationship between impedances at a given frequency?

Phasor diagram

Venn diagram

Near field diagram

Far field diagram



2016-E5C06: What does the impedance 50-j25 represent?

50 ohms resistance in series with 25 ohms capacitive reactance

50 ohms resistance in series with 25 ohms inductive reactance

25 ohms resistance in series with 50 ohms inductive reactance

25 ohms resistance in series with 50 ohms capacitive reactance



2016-E5C07: What is a vector?

A quantity with both magnitude and an angular component

The value of a quantity that changes over time

The inverse of the tangent function

The inverse of the sine function



2016-E5C08: What coordinate system is often used to display the phase angle of a circuit containing resistance, inductive and/or capacitive reactance?

Polar coordinates

Maidenhead grid

Faraday grid

Elliptical coordinates



2016-E5C09: When using rectangular coordinates to graph the impedance of a circuit, what does the horizontal axis represent?

Resistive component

Reactive component

The sum of the reactive and resistive components

The difference between the resistive and reactive components



2016-E5C10: When using rectangular coordinates to graph the impedance of a circuit, what does the vertical axis represent?

Reactive component

Resistive component

The sum of the reactive and resistive components

The difference between the resistive and reactive components



2016-E5C11: What do the two numbers that are used to define a point on a graph using rectangular coordinates represent?

The coordinate values along the horizontal and vertical axes

The magnitude and phase of the point

The sine and cosine values

The tangent and cotangent values



2016-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?

It is equivalent to a pure resistance

It has to be a direct current circuit

It contains resistance and capacitive reactance

It contains resistance and inductive reactance



2016-E5C13: What coordinate system is often used to display the resistive, inductive, and/or capacitive reactance components of impedance?

Rectangular coordinates

Maidenhead grid

Faraday grid

Elliptical coordinates



2016-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?

Point 4

Point 2

Point 5

Point 6



2016-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?

Point 3

Point 1

Point 7

Point 8



2016-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?

Point 1

Point 3

Point 7

Point 8



2016-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?

Point 8

Point 1

Point 3

Point 5






2016-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

2016-E5D01: What is the result of skin effect?

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

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

Thermal effects on the surface of the conductor increase the impedance

Thermal effects on the surface of the conductor decrease the impedance



2016-E5D02: Why is it important to keep lead lengths short for components used in circuits for VHF and above?

To avoid unwanted inductive reactance

To increase the thermal time constant

To maintain component lifetime

All of these choices are correct



2016-E5D03: What is microstrip?

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

Lightweight transmission line made of common zip cord

Miniature coax used for low power applications

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



2016-E5D04: Why are short connections necessary at microwave frequencies?

To reduce phase shift along the connection

To increase neutralizing resistance

Because of ground reflections

To reduce noise figure



2016-E5D05: Which parasitic characteristic increases with conductor length?

Inductance

Permeability

Permittivity

Malleability



2016-E5D06: In what direction is the magnetic field oriented about a conductor in relation to the direction of electron flow?

In a direction determined by the left-hand rule

In the same direction as the current

In a direction opposite to the current

In all directions; omni-directional



2016-E5D07: What determines the strength of the magnetic field around a conductor?

The amount of current flowing through the conductor

The resistance divided by the current

The ratio of the current to the resistance

The diameter of the conductor



2016-E5D08: What type of energy is stored in an electromagnetic or electrostatic field?

Potential energy

Electromechanical energy

Thermodynamic energy

Kinetic energy



2016-E5D09: What happens to reactive power in an AC circuit that has both ideal inductors and ideal capacitors?

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

It is dissipated as heat in the circuit

It is dissipated as kinetic energy in the circuit

It is dissipated in the formation of inductive and capacitive fields



2016-E5D10: How can the true power be determined in an AC circuit where the voltage and current are out of phase?

By multiplying the apparent power times the power factor

By dividing the reactive power by the power factor

By dividing the apparent power by the power factor

By multiplying the reactive power times the power factor



2016-E5D11: What is the power factor of an R-L circuit having a 60 degree phase angle between the voltage and the current?

0.5

1.414

0.866

1.73



2016-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?

80 watts

400 watts

2000 watts

50 watts



2016-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?

100 Watts

70.7 Watts

141.4 Watts

200 Watts



2016-E5D14: What is reactive power?

Wattless, nonproductive power

Power consumed in wire resistance in an inductor

Power lost because of capacitor leakage

Power consumed in circuit Q



2016-E5D15: What is the power factor of an R-L circuit having a 45 degree phase angle between the voltage and the current?

0.707

0.866

1.0

0.5



2016-E5D16: What is the power factor of an R-L circuit having a 30 degree phase angle between the voltage and the current?

0.866

1.73

0.5

0.577



2016-E5D17: How many watts are consumed in a circuit having a power factor of 0.6 if the input is 200VAC at 5 amperes?

600 watts

200 watts

1000 watts

1600 watts



2016-E5D18: How many watts are consumed in a circuit having a power factor of 0.71 if the apparent power is 500VA?

355 W

704 W

252 W

1.42 mW





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