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Subelement A
Principles
Section 3
Materials
What metal is usually employed as a sacrificial anode for corrosion control purposes?
  • Platinum bushing.
  • Lead bar.
  • Correct Answer
    Zinc bar.
  • Brass rod.
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What is the relative dielectric constant for air?
  • Correct Answer
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Dielectric constant, also called relative permittivity or specific inductive capacity, property of an electrical insulating material (a dielectric) equal to the ratio of the capacitance of a capacitor filled with the given material to the capacitance of an identical capacitor in a vacuum without the dielectric material. If C is the value of the capacitance of a capacitor filled with a given dielectric and C0 is the capacitance of an identical capacitor in a vacuum, the dielectric constant, symbolized by the Greek letter kappa, κ, is simply expressed as κ = C/C0. The value of the static dielectric constant of any material is always greater than one, its value for a vacuum. The value of the dielectric constant at room temperature (25 °C, or 77 °F) is 1.00059 for air. Because the value of the dielectric constant for air is nearly the same as that for a vacuum, for all practical purposes air does not increase the capacitance of a capacitor.

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Which metal object may be least affected by galvanic corrosion when submerged in seawater?
  • Aluminum outdrive.
  • Bronze through-hull.
  • Exposed lead keel.
  • Correct Answer
    Stainless steel propeller shaft.
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Skin effect is the phenomenon where:
  • Correct Answer
    RF current flows in a thin layer of the conductor, closer to the surface, as frequency increases.
  • RF current flows in a thin layer of the conductor, closer to the surface, as frequency decreases.
  • Thermal effects on the surface of the conductor increase the impedance.
  • Thermal effects on the surface of the conductor decrease the impedance.
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Corrosion resulting from electric current flow between dissimilar metals is called:
  • Electrolysis.
  • Stray current corrosion.
  • Oxygen starvation corrosion.
  • Correct Answer
    Galvanic corrosion.
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Which of these will be most useful for insulation at UHF frequencies?
  • Rubber.
  • Correct Answer
    Mica.
  • Wax impregnated paper.
  • Lead.
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