  In the framework of the edge-channel picture and the scattering approach to
conduction, we discuss the low frequency admittance of quantized Hall samples
up to second order in frequency. The first-order term gives the leading order
phase-shift between current and voltage and is associated with the displacement
current. It is determined by the emittance which is a capacitance in a
capacitive arrangement of edge channels but which is inductive-like if edge
channels predominate which transmit charge between different reservoirs. The
second-order term is associated with the charge relaxation. We apply our
results to a Corbino disc and to two- and four-terminal quantum Hall bars, and
we discuss the symmetry properties of the current response. In particular, we
calculate the longitudinal resistance and the Hall resistance as a function of
frequency.
