Transmission lines - justification of "wavelength / 10" (or similar) rule
When propagation delay exceeds 10% of wave time , and impedances are not matched throughout, reflections occur which alter the effective input impedance and Ohm's Law.  The amount % depends on system tolerances for return loss, so this is a ballpark figure.

Remember that if the prop delay is 25% of \$\lambda\$ the output impedance if mismatched is inverted at source, ( short becomes open and open becomes short). So Ohm's Law applied to impedance ratios or in other words H(s) transfer functions will be false and more complex equations must be used.

Consider that all conductors ( wires , tracks, leaded parts ) have inductance based on the length to width ratio.  So a perfect conductor rises in impedance with f. and if the applied f starts approaches 10% of λ then its impedance changes rapidly due to reflections.