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Power from current and resistance

Aviation Mechanic General (AMG) practice question 20 of 41 on Fundamentals of Electricity and Electronics. ACS element AM.I.A.K7d · difficulty: applied. Want to answer it in a timed quiz? Use the Aviation Mechanic General (AMG) practice mode.

Question bank updated 2026-09-22

QUESTIONA resistor carries 3 amperes and has a resistance of 50 ohms. What power is dissipated in the resistor?

  1. A450 watts
  2. B150 watts
  3. C16.7 watts, found by dividing 50 by 3
Show the answer and explanation

Correct answer: A. 450 watts

  • A — correct Using the second form of the power equation, P = I squared times R: 3 A squared is 9, and 9 times 50 ohms equals 450 watts.
  • B — incorrect 150 is 3 times 50, which omits squaring the current; the formula requires I squared times R.
  • C — incorrect Dividing resistance by current has no meaning in the power formulas; power is current squared times resistance.

BACKGROUND

Power is the rate of energy consumption or conversion, and in a DC circuit the general power formula is P = I(E). Substituting Ohm's Law (E = IR) gives the second form, P = I squared times R, which uses only current and resistance. Substituting I = E/R gives the third form, P = E squared divided by R. The handbook example uses 2 A and 100 ohms: (2 A) squared times 100 ohms equals 400 W. Power in both series and parallel circuits is additive: the total equals the sum of the power dissipated in each resistor.

STUDY TIP

Write all three power forms on scratch paper before the test: P = IE, P = I squared R, and P = E squared / R.

KEY POINTS

  • P = I squared times R is the power form that uses current and resistance.
  • 3 A squared is 9; 9 times 50 ohms equals 450 W.
  • Total power in a circuit is the sum of the power in each resistor.

SOURCES

  • FAA-H-8083-30B ch12 "Power Formulas Used in the Study of Electricity" > "Second Form of Power Equation"
Practice the Aviation Mechanic General (AMG) test →Timed 60-question exam, by ACS area, or review your misses. Free.
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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.