1. Resistor (R)
Resistors do not change behavior with frequency. No matter the frequency of the signal (low or high), a resistor offers the same resistance.
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Behavior: Constant at all frequencies.
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Use: Controls current flow and voltage drop.
2. Capacitor (C)
A capacitor blocks low-frequency signals and passes high-frequency signals.
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At low frequencies (or DC): Acts like an open circuit (blocks current).
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At high frequencies: Acts like a short circuit (allows current).
Think of it like a frequency gate—only high-frequency signals can get through easily.
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Capacitive Reactance (Xc) = 1 / (2πfC):
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Higher frequency → Lower Xc → Easier for signal to pass.
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Lower frequency → Higher Xc → Harder for signal to pass.
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3. Inductor (L)
An inductor passes low-frequency signals and blocks high-frequency signals.
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At low frequencies (or DC): Acts like a short circuit (easy flow).
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At high frequencies: Acts like an open circuit (resists flow).
Opposite of a capacitor.
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Inductive Reactance (Xl) = 2πfL:
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Higher frequency → Higher Xl → More opposition to signal.
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Lower frequency → Lower Xl → Less opposition.
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4. Filters (Built Using R, L, and C)
Filters are special circuits that selectively pass or block certain frequencies.
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Low-pass filter: Lets low frequencies pass, blocks high ones.
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High-pass filter: Lets high frequencies pass, blocks low ones.
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Band-pass filter: Passes only a range of frequencies.
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Band-stop filter: Blocks a certain range of frequencies.
These are made using combinations of resistors, capacitors, and inductors.
Real-Life Examples
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Speakers: Use filters to send bass to big woofers and treble to tweeters.
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Radios: Use filters to pick out your desired station frequency.
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Power supplies: Use capacitors to block noise (high-frequency signals).
Summary:
| Component | Low Frequency Behavior | High Frequency Behavior |
|---|---|---|
| Resistor | Constant resistance | Constant resistance |
| Capacitor | Blocks (open circuit) | Passes (short circuit) |
| Inductor | Passes (short circuit) | Blocks (open circuit) |
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Capacitor: Blocks low, passes high.
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Inductor: Passes low, blocks high.
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Resistor: Unaffected by frequency.
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Filters: Combine these components to allow or block specific frequencies.
