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block

A toroidal-core coil

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Is ideal as a transmission-line transformer

Works well as a loopstick antenna

Is essentially self-shielding

Has lower inductance than an air-core coil with the same number of turns

Cannot be used at frequencies below about 10 MHz

none

The efficiency of a generator

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Depends on the driving power source

Is equal to driving voltage divided by output voltage

Depends on the nature of the load

Is equal to output power divided by driving power

Is equal to driving current divided by output current

none

The inductance of a coil can be continuously varied by

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Varying the net core permeability

Varying the frequency

Varying the voltage across the coil

Varying the wavelength

Varying the current in the coil

none

The vector 40 + j30 represents

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40 uH inductance and 30 Ω resistance

40 Ω inductive reactance and 30 Ω resistance

40 Ω resistance and 30 μH inductance

40 Ω resistance and 30 Ω inductive reactance

40 uH inductive reactance and 30 Ω resistance

none

Power factor is defined as the ratio of

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True power to imaginary power

Imaginary power to true power

Imaginary power to VA power

VA power to true power

True power to VA power

none

Two complex impedances are in series. One is 30 + j50 and the other is 50 − j30. The net impedance is

Select the correct answer(s).  

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20 - j20

–20 + j20

20 + j20

80 + j20

80 + j80

none

Two inductors, having values of 140 μH and 1.50 mH, are connected in series. The net inductance is

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1.64 mH

0.1415 mH

1.64 μH

0.164 mH

141.5 μH

none

Which of the following types of capacitor is polarized?

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Air variable

Ceramic

Mica

Paper

Electrolytic

none

Admittance is

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A measure of the ease with which a circuit passes ac

Another expression for absolute-value impedance

The reciprocal of resistance

The reciprocal of reactance

A measure of the opposition a circuit offers to ac

none

Which of the following does not affect the capacitance of a capacitor?

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The spacing between the plates (within reason)

The amount of overlap between plates

The mutual surface area of the plates

The dielectric constant of the material between the plates (within reason)

The frequency (within reason)

none

The absolute-value impedance Z of a parallel RLC circuit, where R is the resistance and X is the net reactance, is found according to the formula

Select the correct answer(s).  

(0/0)

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Z2= RX / (R2 + X2)

Z = R2X2/(R + X)

Z2 = R2 + X2

Z = R + X

Z = 1/(R2 + X2)

none

If R denotes resistance and Z denotes absolute-value impedance, then R/Z is the

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True power

Apparent power

Imaginary power

Absolute-value power

Power factor

none

The zero-degree phase point in an ac sine wave is usually considered to be the instant at which the amplitude is

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(0/0)

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Zero and negative-going

Any value; it doesn’t matter

At its negative peak

Zero and positive-going

At its positive peak

none

A 50 Ω feed line needs to be matched to an antenna with a purely resistive impedance of 200 Ω A quarter-wave matching section should have

Select the correct answer(s).  

(0/0)

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Zo = 250 Ω

Zo = 100 Ω

Zo = 133 Ω

Zo = 125 Ω

Zo = 150 Ω

none

Complex numbers are used to represent impedance because

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Engineers like to work with sophisticated mathematics

No! Complex numbers aren’t used to represent impedance

Reactance isn’t a real physical thing

They provide a way to represent what happens in resistance-reactance circuits

Reactance cannot store power