  We discuss predictions of five proposed theories for the critical state of
type-II superconductors accounting for both flux cutting and flux transport
(depinning). The theories predict different behaviours for the ratio $E_y/E_z$
of the transverse and parallel components of the in-plane electric field
produced just above the critical current of a type-II superconducting slab as a
function of the angle of an in-plane applied magnetic field. We present
experimental results measured using an epitaxially grown YBCO thin film
favoring one of the five theories: the extended elliptic critical-state model.
We conclude that when the current density $\bm J$ is neither parallel nor
perpendicular to the local magnetic flux density $\bm B$, both flux cutting and
flux transport occur simultaneously when $J$ exceeds the critical current
density $J_c$, indicating an intimate relationship between flux cutting and
depinning. We also conclude that the dynamical properties of the superconductor
when $J$ exceeds $J_c$ depend in detail upon two nonlinear effective
resistivities for flux cutting ($\rho_c$) and flux flow ($\rho_f$) and their
ratio $r= \rho_c/\rho_f$.
