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Difficulty: HardDirect Current (DC) vs. Alternating Current (AC)

In electrical systems, direct current (DC) and alternating current (AC) exhibit distinct behaviors across chemical, capacitive, magnetic, and electromechanical applications. Match each electrical component or application on the left with its correct operational characteristic regarding AC or DC on the right.

  • Secondary battery charging processRequires unidirectional electron flow to drive chemical reduction and oxidation without periodic reversal
  • Iron-core step-down transformerRelies strictly on continuously varying current to generate changing magnetic flux for mutual induction
  • Capacitor connected across a steady DC sourceActs as an open circuit in steady-state because zero frequency prevents continuous displacement current
  • Split-ring commutator in a rotating generatorMechanically converts an internally generated alternating waveform into pulsating unidirectional output

Answer

Secondary battery charging matches unidirectional chemical restoration; Iron-core transformer matches alternating flux mutual induction; Capacitor in steady DC matches open-circuit behavior at zero frequency; Split-ring commutator matches mechanical rectification of AC to DC.
Each component is correctly matched to its fundamental AC or DC operating mechanism: battery charging requires unidirectional DC electron flow for chemical storage, transformers depend on AC-induced time-varying magnetic flux, capacitors block steady DC at 0 Hz0\text{ Hz}, and commutators mechanically rectify internally induced AC into DC.

Step-by-Step Solution

1
Analyze the chemical requirement of battery charging
Battery charging requires continuous direct current (DC) so that ions travel consistently toward their designated electrodes without reversing every half-cycle.
AC would alternate between charging and discharging every cycle, resulting in zero net chemical energy storage.
2
Analyze transformer operational physics
Transformers require alternating current (AC) to produce a continuously changing magnetic field (ΔΦ/Δt\Delta\Phi/\Delta t) across the core to induce an electromotive force in the secondary coil.
Steady DC produces a static magnetic field that cannot induce continuous secondary voltage.
3
Analyze capacitive reactance under DC conditions
With capacitive reactance XC=12πfCX_C = \frac{1}{2\pi f C}, a steady DC source has a frequency of f=0 Hzf = 0\text{ Hz}, yielding infinite reactance (XC→∞X_C \rightarrow \infty) once charged.
Direct current cannot cross the insulating dielectric layer once charge equilibrium is established.
4
Analyze the electromechanical function of a split-ring commutator
Rotating loops in a magnetic field inherently produce AC; the split rings reverse contact connections at each half-rotation, converting internal AC into pulsating DC.
The commutator serves as a mechanical rectifier.

Key Concept

Fundamental distinctions in how alternating current (time-varying direction/magnitude) and direct current (unidirectional flow) govern induction, electrochemistry, capacitive opposition, and mechanical waveform rectification.
Estimated Time:1m 30s
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Topics

Direct Current (DC) vs. Alternating Current (AC)

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