In a double-slit experiment, the fourth-order maximum for a wavelength of 450 nm occurs at an angle of θ = 90°.
(a) What range of wavelengths in the visible range (400 nm to 700 nm) are not present in the third-order maxima? To eliminate all visible light in the fourth-order maximum,
(b) Should the slit separation be increased or decreased
(c) What least change is needed?