Electrons cannot follow the applied A.C field

[photon79]

what does it really mean by saying that "electrons cannot follow the applied A.C field!" ?? (hence the wave vector is complex!)

 

[armandowww]

are you talking about high frequency phenomena? Would you give us any additive explanations?

 

[Gokul43201]

what does it really mean by saying that "electrons cannot follow the applied A.C field!" ?? (hence the wave vector is complex!)

Please state the source.