Light of wavelength 489 nm incident on a pair of slits produces an interference pattern on a distant screen in which the separation between adjacent bright fringes at the center of the pattern is 0.509 cm. A second light source, when incident on the same pair of slits, produces an interference pattern on the same screen with a separation of 0.646 cm between adjacent bright fringes at the center of the pattern. What is the wavelength of the second source? [Hint: Is the small angle approximation justified?]