# Gibilisco - Transformers And Impedance Matching

20 Questions | Total Attempts: 490  Settings  • 1.
In a step-up transformer,
• A.

The primary impedance is greater than the secondary impedance.

• B.

The secondary winding is right on top of the primary.

• C.

The primary voltage is less than the secondary voltage.

• D.

All of the above are true.

• 2.
The capacitance between the primary and the secondary windings of a transformer can beminimized by
• A.

Placing the windings on opposite sides of a toroidal core.

• B.

Winding the secondary right on top of the primary.

• C.

Using the highest possible frequency.

• D.

Using a center tap on the balanced winding.

• 3.
A transformer steps a voltage down from 117 V to 6.00 V. What is its primary-to-secondaryturns ratio?
• A.

1:380

• B.

380:1

• C.

1:19.5

• D.

19.5:1

• 4.
A step-up transformer has a primary-to-secondary turns ratio of 1:5.00. If 117 V rms appearsat the primary, what is the ac rms voltage across the secondary?
• A.

23.4 V rms

• B.

585 V rms

• C.

117 V rms

• D.

2.93 kV rms

• 5.
A transformer has a secondary-to-primary turns ratio of 0.167. This transformer is
• A.

A step-up unit.

• B.

A step-down unit.

• C.

Neither a step-up unit nor a step-down unit.

• D.

A reversible unit.

• 6.
Which of the following statements is false, concerning air cores compared with ferromagneticcores?
• A.

Air concentrates the magnetic lines of flux.

• B.

Air works at higher frequencies than ferromagnetics.

• C.

Ferromagnetics are lossier than air.

• D.

A ferromagnetic-core transformer needs fewer turns of wire than an equivalent air-core transformer.

• 7.
Eddy currents cause
• A.

An increase in efficiency.

• B.

An increase in coupling between windings.

• C.

An increase in core loss.

• D.

An increase in usable frequency range.

• 8.
Suppose a transformer has an ac voltage of 117 V rms across its primary, and 234 V rmsappears across its secondary. If this transformer is reversed (that is, connected backward), assuming that this be done without damaging the windings, what will be the voltage at the output?
• A.

234 V rms

• B.

468 V rms

• C.

117 V rms

• D.

58.5 V rms

• 9.
The shell method of transformer winding
• A.

Provides maximum coupling.

• B.

Minimizes capacitance between windings.

• C.

Withstands more voltage than other winding methods.

• D.

Has windings far apart but along a common axis.

• 10.
Which of these core types is best if you need a winding inductance of 1.5 H?
• A.

Air core

• B.

Ferromagnetic solenoid core

• C.

Ferromagnetic toroid core

• D.

Ferromagnetic pot core

• 11.
An advantage of a toroid core over a solenoid core is the fact that
• A.

The toroid works at higher frequencies.

• B.

The toroid confines the magnetic flux.

• C.

The toroid can work for dc as well as for ac.

• D.

It is easier to wind the turns on a toroid.

• 12.
High voltage is used in long-distance power transmission because
• A.

It is easier to regulate than low voltage.

• B.

The I^2 R losses are minimized.

• C.

The electromagnetic fields are strong.

• D.

Small transformers can be used.

• 13.
In a household circuit, 234-V rms electricity usually has
• A.

One phase.

• B.

Two phases.

• C.

Three phases.

• D.

Four phases.

• 14.
In a transformer, a center tap often exists in
• A.

The primary winding.

• B.

The secondary winding.

• C.

An unbalanced winding.

• D.

A balanced winding.

• 15.
An autotransformer
• A.

• B.

Has a center-tapped secondary.

• C.

Consists of a single tapped winding.

• D.

Is useful only for impedance matching.

• 16.
Suppose a transformer has a primary-to-secondary turns ratio of 2.00:1. The inputimpedance is 300 Ω, purely resistive. What is the output impedance?
• A.

75 Ω, purely resistive

• B.

150 Ω, purely resistive

• C.

600 Ω, purely resistive

• D.

1200 Ω, purely resistive

• 17.
Suppose a purely resistive input impedance of 50 Ω must be matched to a purely resistiveoutput impedance of 450 Ω. The primary-to-secondary turns ratio of the transformer must bewhich of the following?
• A.

9.00

• B.

3.00

• C.

1/3.00

• D.

1/9.00

• 18.
Suppose a quarter-wave matching section has a characteristic impedance of 75.0 Ω. Theinput impedance is 50.0 Ω, purely resistive. What is the output impedance?
• A.

150 Ω, purely resistive

• B.

125 Ω, purely resistive

• C.

100 Ω, purely resistive

• D.

113 Ω, purely resistive

• 19.
Suppose a purely resistive impedance of 75 Ω must be matched to a purely resistiveimpedance of 300 Ω. A quarter-wave section would need to have
• A.

Zo = 188 Ω.

• B.

Zo = 150 Ω.

• C.

Zo = 225 Ω.

• D.

Zo = 375 Ω.

• 20.
If there is reactance in the load to which a transformer is connected, then
• A.

The transformer will be destroyed.

• B.

A perfect impedance match cannot be obtained.

• C.

A center tap must be used in the secondary.

• D.

The turns ratio must be changed to obtain an impedance match.

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