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ASVAB · Circuits and Ohm's Law

In a series circuit with resistors of 10 Ω, 20 Ω, and 30 Ω, what is the total resistance?

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Correct answer

60 Ω

  1. A 60 Ω
  2. B 10 Ω
  3. C 30 Ω
  4. D 6 Ω

Why this is the answer

In a series circuit, resistances add: R_total = 10 + 20 + 30 = 60 Ω. In series there is only one path for current, so every resistor adds to the total opposition and the total is always larger than the largest single resistor. The distractor 6 Ω is what you would get from the parallel formula (1/10 + 1/20 + 1/30 inverted ≈ 5.45 Ω, rounded) — in parallel the total is always smaller than the smallest resistor. 10 Ω and 30 Ω are just single resistors from the list.
Source: ASVAB EI, Series Circuits

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About this topic: Circuits and Ohm's Law

Circuits and Ohm's Law questions ask you to calculate voltage, current, resistance or power, and to understand series versus parallel circuits — how resistance adds in series and reduces in parallel, and what happens when one component fails. This is one of 17 Electronics Information questions on circuits and ohm's law, each with a full explanation on a single study page.

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