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Difficulty: EasyInductors and Transformers

A technician installs an inductor (choke) in series with the output line of a direct current (DC) power supply to filter out residual alternating current (AC) ripple. What is the primary effect of the inductor on this electrical current?

  1. A
    It completely blocks steady direct current while allowing alternating current ripple to pass freely.
  2. B
    It steps up the fluctuating AC voltage into a higher voltage DC output through mutual induction.
  3. It opposes rapid changes in current, resisting the AC ripple while allowing steady DC to pass with minimal resistance.Answer
  4. D
    It dissipates both AC ripple and steady DC current equally as thermal heat by acting as a pure resistor.

Answer

The inductor opposes rapid current variations (the AC ripple) due to inductive reactance while allowing steady direct current (DC) to pass freely.
An inductor resists changes in current through self-induction. When placed in series with a DC power supply line, its inductive reactance (XL=2πfLX_L = 2\pi f L) creates significant opposition to the fluctuating AC ripple component while providing near-zero opposition to the constant DC current.

Step-by-Step Solution

1
Identify the fundamental operating principle of an inductor.
Inductors store energy in a magnetic field and inherently oppose any change in electrical current (VL=LdidtV_L = L \frac{di}{dt}).
According to Lenz's Law, when current changes through a coil, a self-induced counter-electromotive force (CEMF) is produced that resists that change.
2
Analyze the inductor's frequency-dependent opposition (inductive reactance, XLX_L).
For steady DC (f=0 Hzf = 0\text{ Hz}), XL=2πfL=0 ΩX_L = 2\pi f L = 0\,\Omega, so DC passes with negligible opposition. For AC ripple (f>0 Hzf > 0\text{ Hz}), XL>0 ΩX_L > 0\,\Omega, which impedes the fluctuation.
Higher frequency signals encounter significant inductive reactance, attenuating the unwanted AC ripple while letting constant DC through to the load.

Key Concept

Inductors oppose changes in alternating current via inductive reactance while allowing steady direct current to flow with minimal opposition.
Estimated Time:45s
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Topics

Inductors and Transformers

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