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Subel. ZLB
10 questions
Subelement ZLB

Basic Electrical Theory

Section ZLB08

Alternating Current

An 'alternating current' is so called because

  • Correct Answer
    it reverses direction periodically
  • it travels through a circuit using alternate paths
  • its direction of travel is uncertain
  • its direction of travel can be altered by a switch

Alternating current is called so because the electrons carried by the current move back & forth creating a wave. Alternating direction. Depending on where you are in the world, the number of times per second this wave occurs varies. Each wave, or cycle, back & forth is called a Hertz (Hz).

In New Zealand, our electrical current normally operates at 50Hz.

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The time for one cycle of a 100 Hz signal is

  • 1 second
  • Correct Answer
    0.01 second
  • 0.0001 second
  • 10 seconds
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A 50 hertz current in a wire means that

  • a potential difference of 50 volts exists across the wire
  • the current flowing in the wire is 50 amperes
  • the power dissipated in the wire is 50 watts
  • Correct Answer
    a cycle is completed 50 times in each second
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The current in an AC circuit completes a cycle in 0.1 second. So the frequency is

  • 1 Hz
  • Correct Answer
    10 Hz
  • 100 Hz
  • 1000 Hz
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An impure signal is found to have 2 kHz and 4 kHz components. This 4 kHz signal is

  • a fundamental of the 2 kHz signal
  • a sub-harmonic of 2 kHz
  • the DC component of the main signal
  • Correct Answer
    a harmonic of the 2 kHz signal
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The correct name for the equivalent of 'one cycle per second' is one

  • henry
  • volt
  • Correct Answer
    hertz
  • coulomb
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One megahertz is equal to

  • 0.0001 Hz
  • 100 kHz
  • Correct Answer
    1000 kHz
  • 10 Hz
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One GHz is equal to

  • 1000 kHz
  • 10 MHz
  • 100 MHz
  • Correct Answer
    1000 MHz
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The 'rms value' of a sine-wave signal is

  • half the peak voltage
  • 1.414 times the peak voltage
  • the peak-to-peak voltage
  • Correct Answer
    0.707 times the peak voltage
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A sine-wave alternating current of 10 ampere peak has an rms value of

  • 5 amp
  • Correct Answer
    7.07 amp
  • 14.14 amp
  • 20 amp
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