Tests of the standard model and constraints on new physics from measurements of fermion-pair production at 189 GeV at LEP

Cross-sections and angular distributions for hadronic and lepton pair final states in e(+) e(-) collisions at a centre-of-mass energy near 189 GcV. 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 bq the exchange of a new heavy particle such as a sneutrino in super symmetric 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 ia also presented.