Consider a nuclear experiment involving an alpha particle. This alpha particle is set to traverse a region between two parallel-plate electrodes. These electrodes are 1.5 cm long and are separated by a distance of 2.0 mm. At a right angle to the electric field produced by these electrodes, there exists a magnetic field. This magnetic field has a strength of 1.0 mT and extends across a width of 1.5 cm. The alpha particle is able to navigate through the electrodes without experiencing any deflection, but this is only possible when the potential difference across the electrodes is maintained at 400 V. Given this setup, (i) calculate the speed at which the alpha particle is moving, and (ii) if the potential difference between the plates is set to zero, determine the alpha particle's radius of curvature in the magnetic field.