30×103,30×103Ionization energy E1​∝[121​−∝1​]E1​=40keVMinimum energy to produce X-rays in the transition forn=2 to n=1 isE2​∝[121​−221​]From equations (i) and (ii), we getE2​=43​E1​=30keVTherefore minimum voltage required is 30keV or 30×103 V and the energy of characteristic radiation will be, 30keV or 30×103eV.