The characteristic impedance of a 20-metre piece of transmission line is 52 ohms. What would the impedance be if 10 metres were cut off?

Characteristic impedance is a fixed property of a transmission line's physical cross-section, determined by the spacing between conductors and the type of insulating dielectric used. It represents the ratio of voltage to current in a forward-traveling wave. Because it is determined by the cable's geometry and internal materials rather than its length, altering the length of the cable does not change its characteristic impedance. Therefore, whether the line is 20 metres or 10 metres long, a 52-ohm cable remains exactly 52 ohms.