Electronic Principles – Section 1

16. Which one of the following statements best describes magnetic hysteresis?

A. Hysteresis is the amount of magnetic flux that is not confined to the core material of an electromagnet
B. Hysteresis is most apparent when a steady amount of current is lowing through the coil of an electromagnet
C. Hysteresis is most apparent when the current through the coil of an electromagnet changes frequently
D. Hysteresis is most apparent when the core material is saturated
E. None of the above

Correct Answer:  C. Hysteresis is most apparent when the current through the coil of an electromagnet changes frequently

17. Which one of the following phrases best describes residual magnetism?

A. Magnetism that remains in the core of an electromagnet after the current through the coil is turned off
B. The force of attraction between the poles of a permanent and temporary magnetic field
C. The amount of magnetic flux that is not confined to the core material of an electromagnet
D. The circular magnetic field that surrounds a conductor carrying a current
E. None of the above

Correct Answer:  A. Magnetism that remains in the core of an electromagnet after the current through the coil is turned off

18. A transformer has a primary voltage of 120 V rms and a secondary voltage of 25 V rms. If the secondary
current is 1A rms, what is the primary current?

A. 7.8 mA
B. 208 mA
C. 200 mA
D. 300 mA
E. None of the above

Correct Answer:  B. 208 mA

19. Household light bulbs have a given power rating, and they operate at 120 V. Which one of the following equations most directly provides the current rating of these light bulbs?

A. P = I2R
B. P = IE
C. P = E2 /R
D. I = P/E
E. None of the above

Correct Answer:  D. I = P/E

20. Which one of the following phrases most accurately describes a purely inductive circuit?

A. Resistances provide the only opposition to current flow
B. Inductive reactance provides the only opposition to current flow
C. Combinations of resistance and inductive reactance provide any opposition to current flow
D. The ac voltage lags the current by 90 degree
E. None of the above

Correct Answer:  B. Inductive reactance provides the only opposition to current flow

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