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Resistance versus cross-sectional area

Aviation Mechanic General (AMG) practice question 9 of 41 on Fundamentals of Electricity and Electronics. ACS element AM.I.A.K11a · difficulty: standard. Want to answer it in a timed quiz? Use the Aviation Mechanic General (AMG) practice mode.

Question bank updated 2026-09-22

QUESTIONA conductor is replaced with one of the same material, length, and temperature but with twice the cross-sectional area. What happens to its resistance?

  1. AIt doubles
  2. BIt is reduced to one-half
  3. CIt stays the same because length is unchanged
Show the answer and explanation

Correct answer: B. It is reduced to one-half

  • A — incorrect Doubling the length would double the resistance; doubling the area has the opposite effect.
  • B — correct Resistance is inversely proportional to cross-sectional area; doubling the area cuts the resistance to current flow in half.
  • C — incorrect Area is one of the four factors that determine resistance; changing it changes the resistance even when length is fixed.

BACKGROUND

The resistance of a metallic conductor is determined by four properties: material, length, cross-sectional area, and temperature. Resistance is directly proportional to length, so a wire twice as long has twice the resistance. It is inversely proportional to cross-sectional area, so doubling the area reduces the resistance by half because electrons have more room to move without collision. Most conductor materials increase in resistance as temperature rises, described by the temperature coefficient of resistance. In the American wire gauge system, a decrease of three gauge numbers roughly doubles the area and cuts the resistance of a given length in half.

STUDY TIP

Keep the two proportions straight: resistance goes up with length and down with area.

KEY POINTS

  • Resistance depends on material, length, area, and temperature.
  • Doubling the cross-sectional area halves the resistance.
  • Doubling the length doubles the resistance.

SOURCES

  • FAA-H-8083-30B ch12 "Factors Affecting Resistance" (item 3)
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SkyDrill is not affiliated with the FAA. This is an original practice item based on FAA-H-8083-30B Aviation Maintenance Technician Handbook – General, 14 CFR part 43 and part 65. Regulations and handbooks are revised; confirm details against the current edition.