Video narration
When a voltage pulse enters a long cable, it doesn’t appear everywhere at once. It travels down the line as an electromagnetic wave, carrying voltage and current together. On that traveling wave, the ratio V divided by I is fixed: the line’s characteristic impedance, Z0. At the load, the wave “asks”: can I deliver my power into this impedance? If the load equals Z0, the energy is absorbed and the wave ends there—no reflection. But if the load impedance is different, the boundary can’t satisfy the needed voltage and current at the same time, so a second wave is launched back toward the source: the reflection. An open circuit can’t take current, so the reflected voltage has the same polarity and adds, making the end voltage nearly double. A short circuit forces the end voltage to zero, so the reflected voltage flips polarity and cancels. We summarize this with the reflection coefficient, Γ: its size tells how much reflects, and its sign tells whether the voltage adds or inverts. That’s why impedance matching matters in communication cables, RF circuits, and even power-system traveling-wave protection.