Difficulty: Easy
Correct Answer: 82 Ω
Explanation:
Introduction / Context:
Ohm’s law (V = I * R) is the cornerstone of basic circuit calculations. When voltage and current are known, resistance follows directly. This is common when setting rheostats or selecting series resistors to achieve a target current.
Given Data / Assumptions:
Concept / Approach:
Solve the rearranged Ohm’s law: R = V / I. Convert milliampere to ampere to avoid unit errors. Round to a standard-ohmic value if needed for options.
Step-by-Step Solution:
Verification / Alternative check:
Back-calculate current: I = V / R = 18 / 82 ≈ 0.2195 A = 219.5 mA, which is consistent with the given 220 mA.
Why Other Options Are Wrong:
8.2 kΩ and 820 Ω would yield currents far smaller than 220 mA. 8.2 Ω would give I ≈ 2.2 A, much larger than specified.
Common Pitfalls:
Forgetting to convert mA to A; misplacing decimals; using R = I / V instead of R = V / I.
Final Answer:
82 Ω
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