  Cross-sections and angular distributions for hadronic and lepton pair final
states in e+e- collisions at a centre-of-mass energy near 189 GeV, measured
with the OPAL detector at LEP, are presented and compared with the predictions
of the Standard Model. The results are used to measure the energy dependence of
the electromagnetic coupling constant alpha_em, and to place limits on new
physics as described by four-fermion contact interactions or by the exchange of
a new heavy particle such as a sneutrino in supersymmetric theories with
R-parity violation. A search for the indirect effects of the gravitational
interaction in extra dimensions on the mu+mu- and tau+tau- final states is also
presented.
