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Difficulty: MediumCapacitors

In a multi-stage radio receiver, an electronics technician places a coupling capacitor in series along the signal line between two amplifier stages. What is the primary function of this capacitor regarding the combined Direct Current (DC) bias and Alternating Current (AC) signal?

  1. A
    Allows the continuous DC bias to pass freely while completely stopping all fluctuating AC signal frequencies.
  2. Permits the fluctuating AC signal to pass through while completely blocking the steady DC bias voltage.Answer
  3. C
    Transforms the AC signal into a higher DC voltage by generating a strong magnetic field across its plates.
  4. D
    Conducts the steady DC voltage directly across its dielectric material while dissipating the AC signal as heat.

Answer

Permits the fluctuating AC signal to pass through while completely blocking the steady DC bias voltage.
A capacitor acts as an open circuit to steady Direct Current (DC) because the insulating dielectric stops continuous charge conduction once the plates reach the bias voltage level. Simultaneously, the alternating fluctuations of an AC signal continuously charge and discharge the plates, allowing the alternating signal to transfer cleanly to the next amplifier stage without shifting its DC bias point.

Step-by-Step Solution

1
Analyze capacitor behavior in a steady Direct Current (DC) state.
Because the dielectric layer is an electrical insulator, steady DC charges the plates until the potential difference equals the supply voltage, reducing steady-state current to zero (XC=∞X_C = \infty at 0 Hz0\text{ Hz}). The capacitor acts as an open circuit to DC.
Determines how the DC operating bias of the first amplifier stage is isolated from the second stage.
2
Analyze capacitor behavior when exposed to an Alternating Current (AC) signal.
The alternating polarity causes continuous charging and discharging cycles, allowing the AC signal to transfer across the component with low capacitive reactance (XC=12πfCX_C = \frac{1}{2\pi f C}).
Determines how dynamic information and audio/RF waveforms propagate across the circuit.
3
Evaluate the combined circuit function of a series coupling capacitor.
The component blocks the steady DC bias voltage while coupling the alternating signal waveform directly to the next amplifier stage.
Confirms the core operational role of coupling capacitors in electronic signal chains.

Key Concept

Capacitor DC Blocking and AC Coupling
Estimated Time:1m 0s
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Topics

Capacitors

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