Capacitive reactance comparison at 60 Hz: given two capacitors, 10 µF and 20 µF, which one has the larger capacitive reactance magnitude Xc in a 60 Hz AC circuit?

Difficulty: Easy

Correct Answer: 10 µF has the larger reactance

Explanation:


Introduction / Context:
Capacitive reactance determines how strongly a capacitor opposes AC. Understanding how Xc depends on C and frequency helps in filter design and impedance matching.


Given Data / Assumptions:

  • Frequency f = 60 Hz.
  • Capacitances: 10 µF and 20 µF.
  • Ideal components; ESR and ESL neglected.


Concept / Approach:
Capacitive reactance is Xc = 1 / (2 * pi * f * C). For fixed f, Xc is inversely proportional to C. Therefore, the smaller capacitor (10 µF) exhibits the larger reactance magnitude; the larger capacitor (20 µF) has half that reactance.


Step-by-Step Solution:

1) Xc(10 µF) = 1 / (2 * pi * 60 * 10e-6) ≈ 265.3 Ω. 2) Xc(20 µF) = 1 / (2 * pi * 60 * 20e-6) ≈ 132.7 Ω. 3) Compare: 265.3 Ω > 132.7 Ω, so 10 µF has larger reactance.


Verification / Alternative check:
Doubling C halves Xc at fixed frequency, consistent with the formula.


Why Other Options Are Wrong:
“20 µF larger / equal / independent of C / infinite at 60 Hz” each contradicts Xc = 1/(2*pi*f*C).


Common Pitfalls:
Mixing resistance with reactance; forgetting to convert microfarads to farads.


Final Answer:
10 µF has the larger reactance

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