- #1

eyeweyew

- 27

- 5

- TL;DR Summary
- If the parasitic capacitor needs to be charged up one by one along the transmission line in order for voltage to propagate, then how can current be so much slower than propagation?

I am a bit confused on the speed of voltage propagation in the transmission line and I hope someone can enlighten me. I understand the speed of voltage propagation is in the same order as the speed of light and it is much faster than current. But if we can model the transmission line with a distributed LC model as the image attached, how can the modelled capacitors got charged so fast at a rate proportional to the speed of voltage propagation if an electron travel much slower? In other words, voltage propagation requires capacitor to be charged up one after another along the transmission line according to the model. If this is the case, that means electrons need to travelling from the + side to the - side in order to charge a capacitor but if electron is indeed traveling very slowly then how can voltage propagate that fast in the transmission line?

Image source: https://www.allaboutcircuits.com/textbook/alternating-current/chpt-14/characteristic-impedance/

Image source: https://www.allaboutcircuits.com/textbook/alternating-current/chpt-14/characteristic-impedance/