Full-wave rectifier output polarity: In a properly wired full-wave rectifier, the current through the load resistor flows ______ over time.
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Ain opposite directions
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Bto the external load
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Cfrom the reverse biased diode
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Din the same direction
Answer
Correct Answer: in the same direction
Explanation
Introduction / Context:Full-wave rectification is designed to convert both halves of an AC waveform into unidirectional current through the load, improving efficiency and reducing filter requirements compared with half-wave rectification. Understanding load current direction is fundamental to predicting ripple and sizing capacitors.
Given Data / Assumptions:
- Full-wave rectification via either a center-tapped two-diode circuit or a bridge rectifier.
- Ideal diodes for conceptual clarity.
- Resistive load.
Concept / Approach:Each half-cycle of AC is routed so that the load always sees the same polarity. In a bridge, two diodes conduct on the positive half-cycle and the other two on the negative half-cycle, but current through the load keeps the same direction. In the center-tapped scheme, one diode conducts per half-cycle to maintain the same load polarity. Thus, the load current direction is constant over time (though its magnitude pulsates).
Step-by-Step Solution:
Track conduction paths for the positive half-cycle and note load current direction.Track conduction paths for the negative half-cycle; different diodes conduct, but load polarity is unchanged.Conclude that the load current flows in the same direction for both halves.Verification / Alternative check:Oscilloscope across the load shows a pulsating DC waveform that never reverses polarity. After adding a filter capacitor, ripple decreases, but polarity remains the same.
Why Other Options Are Wrong:
- Opposite directions: That describes AC directly across the load (no rectifier).
- ”From the reverse-biased diode”: Reverse-biased diodes do not conduct.
- ”To the external load”: Vague and does not address directionality.
Common Pitfalls:Assuming current direction alternates because the input is AC; the rectifier topology specifically prevents this at the load.
Final Answer:in the same direction