  We study stationary electron flow through a three-terminal quantum ring and
describe effects due to deflection of electron trajectories by classical
magnetic forces. We demonstrate that generally at high magnetic field ($B$) the
current is guided by magnetic forces to follow a classical path which for $B>0$
leads via the left arm of the ring to the left output terminal. The transport
to the left output terminal is blocked for narrow windows of magnetic field for
which the interference within the ring leads to formation of wave functions
that are only weakly coupled to the output channel wave functions. These
interference conditions are accompanied by injection of the current to the
right arm of the ring and by appearance of sharp peaks of the transfer
probability to the right output terminal. We find that these peaks at high
magnetic field are attenuated by thermal widening of the transport window. We
also demonstrate that the interference conditions that lead to their appearance
vanish when an elastic scattering within the ring is present. The clear effect
of magnetic forces on the transfer probabilities disappears along with
Aharonov-Bohm oscillations in a chaotic transport regime that is found for
rings whose width is larger than the width of the channels.
