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Ohm's Law in circuit troubleshooting

Aviation Mechanic Airframe (AMA) practice question 16 of 24 on Aircraft Electrical Systems. ACS element AM.II.K.K12 · difficulty: applied. Want to answer it in a timed quiz? Use the Aviation Mechanic Airframe (AMA) practice mode.

Question bank updated 2026-09-22

QUESTIONA 28-volt landing light circuit has a lamp with 4 ohms of resistance. What is the total current in the circuit?

  1. A112 amps
  2. B0.14 amp
  3. C7 amps
Show the answer and explanation

Correct answer: C. 7 amps

  • A — incorrect This multiplies voltage by resistance instead of dividing, which solves for the wrong quantity.
  • B — incorrect This divides the resistance by the voltage, inverting the correct relationship.
  • C — correct Current equals voltage divided by resistance, so 28 volts divided by 4 ohms gives 7 amps.

BACKGROUND

Ohm's Law states that E equals I times R, where E is electromotive force in volts, I is current in amperes, and R is resistance in ohms, and the formula can be rearranged to solve for current or resistance. Whenever troubleshooting aircraft electrical circuits it is valuable to consider Ohm's Law, because understanding the relationship between resistance and current helps determine whether a circuit contains an open or a short. Remembering that low resistance means increased current helps explain why circuit breakers pop or fuses blow. In almost all cases aircraft loads are wired in parallel, so a constant voltage is supplied to all loads and the current through each load depends on that load's resistance. A 28-volt circuit with a 4-ohm lamp therefore draws 7 amps.

STUDY TIP

Set the division up before you look at the numbers offered: current is volts over ohms, and a sanity check is that the answer must be smaller than the voltage figure here.

KEY POINTS

  • Ohm's Law links voltage, current, and resistance as E equals I times R.
  • Current equals voltage divided by resistance.
  • A 28-volt circuit through 4 ohms carries 7 amps.

SOURCES

  • sources/ama-airframe/ch09.txt "Ohm's Law" Example 1
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MORE ON AIRCRAFT ELECTRICAL SYSTEMS

SkyDrill is not affiliated with the FAA. This is an original practice item based on FAA-H-8083-31B Aviation Maintenance Technician Handbook – Airframe, and 14 CFR part 43. Regulations and handbooks are revised; confirm details against the current edition.