Two lasers are shining on a double slit, with slit separation d. Laser one has a wavelength of d/20, while laser two has a wavelength of d/15 . The lasers produce separate interference patterns on a screen a large distance L away from the slits. Which laser has its first maximum closer to the central maximum? I read that the first maximum comes when the path difference between the two slits is equal to one full wavelength. What does this have to do with the laser that has a smaller wavelength (laser 1)? The distance from the central maximum is proportional to the path-difference, but I stiill don't understand exactly what the central maximum is. Any help is appreciated.