In electronics, we often talk about resistance, capacitance, impedance, and phase shift — especially when working with AC signals or digital electronics like microcontrollers. These terms can seem confusing at first, but they all connect beautifully once you understand their basic meanings.
Let’s break them down in simple, everyday language.
๐ What Is Resistance?
Resistance is the most basic and familiar idea. It simply means how much a component opposes the flow of electrical current. It works the same way for DC (direct current) and AC (alternating current).
Think of resistance like a narrow pipe in a water system — it limits how much water (current) can flow through. This opposition is measured in ohms (ฮฉ).
๐ What Is Impedance?
Impedance is like the AC version of resistance.
When you send AC signals, the current keeps changing direction — it goes back and forth. In this case, resistance alone is not enough to describe how the circuit behaves. That's where impedance comes in.
Impedance includes:
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Resistance (the same kind from before)
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Reactance (a new kind of opposition that depends on the signal’s frequency)
So, impedance is the total "opposition" a circuit gives to an AC signal — it's made of both resistance and reactance.
๐ What Is Reactance?
Reactance is the part of impedance that comes from components like capacitors and inductors.
These don’t behave like simple resistors. Instead, they store and release energy as the current changes. This causes two important things:
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They oppose AC flow, but the amount depends on the frequency of the signal.
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They shift the timing of the voltage or current (this is called phase shift).
There are two types of reactance:
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Capacitive Reactance – from capacitors (stronger at low frequencies)
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Inductive Reactance – from inductors (stronger at high frequencies)
⚙️ What Is Capacitance?
A capacitor stores energy in an electric field. It:
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Blocks DC (after charging up)
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Slows down voltage changes in AC
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Reacts more at lower frequencies
The more capacitance, the longer it can store energy before it’s “full.”
๐ What Is Inductance?
An inductor stores energy in a magnetic field. It:
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Passes DC easily (after a while)
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Slows down current changes in AC
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Reacts more at higher frequencies
The more inductance, the more it resists rapid changes in current.
⏱ What Is Phase Shift?
When capacitors and inductors react to changing signals, they cause a delay in current or voltage.
This is called a phase shift. It means the output wave is still a sine wave, but it starts a little later (or earlier) than the input.
The shape stays the same, but it's shifted in time.
๐งฐ What Is an RLC Circuit?
An RLC circuit has:
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A Resistor (R)
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An Inductor (L)
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A Capacitor (C)
Together, they create interesting effects like:
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Filtering certain frequencies
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Resonance, where the circuit amplifies a specific frequency
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Phase shifts
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Damping (signal fading over time)
At the right frequency (called the resonant frequency), the inductor and capacitor cancel each other’s reactance, and the circuit allows the maximum current to flow.
๐ง Impedance in Digital Electronics
In digital or microcontroller circuits, when we say a pin is set to high impedance, it means:
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The pin is not pushing or pulling any current.
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It’s like the pin is disconnected or in “listen-only” mode.
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This is useful for input pins or when sharing a wire (like I2C or SPI).
In this context, impedance just means very high resistance, not AC behavior.
⚡ Impedance in DC Circuits?
In pure DC circuits:
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Capacitors block DC (after charging up)
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Inductors act like normal wires after a while
So in DC, impedance is basically just resistance. We don’t really use the full concept of impedance unless the signal is changing — like AC or high-speed digital pulses.
๐งช Final Thought: Why It Matters
Understanding impedance and how it connects resistance, reactance, capacitance, and inductance helps you:
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Design filters, amplifiers, and oscillators
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Tune circuits to specific frequencies
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Know why digital pins are “floating” or “high-Z”
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Avoid mistakes when mixing analog and digital signals
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