Question about mosfet parameters

I have some doubts about mosfet K' and lambda. For an nmos:

1)K'=u*C'ox with u=electron mobility;u=Vdrift/E with E=electric field=Vds/L......K' should depends on L, but why it depends also on W? 2)channel lenght modulation parameter (lambda) depends only on L or (fixed L) depends also on W? Thanks for he help