The Bohr model, although not strictly applicable, can be used to estimate the minimum energy Emin that an incoming electron must have in an X-ray tube in order to knock a K-shell electron entirely out of an atom in the metal target. The Ka X-ray wavelength of metal A is 2.0 times the Ka X-ray wavelength of metal B. What is the ratio of Emin, A for metal A to Emin, B for metal B?