Gibilisco - Transformers And Impedance Matching

20 Questions | Total Attempts: 490

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Transformers Quizzes & Trivia

Questions and Answers
  • 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. 

      Can be adjusted automatically.

    • 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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