If voltage applied to an X-ray tube is increased from V = 10 kV to 20 kV, the wave length interval between Kα -line and cut off wavelength of  continuous X-ray becomes three times. Take  Rhce=13.6V,hc=12420  (eV−A°), where R is Rydberg constant, h is Planck's constant, c is speed of light in vacuum and -e is charge on electron.Mark the CORRECT statement(s).