A parallel plate capacitor contains a mica sheet (thickness =10−3 m) and a sheet of fibre (thickness =0.5×10−3 m). The dielectric constant of mica is 8 and that of fibre is 2.5. Assuming that the fibre breaks down when subjected to an electric field of 6.4×106 V/m, find the maximum safe voltage that can be applied to the capacitor.