In a single slit diffraction experiment first minimum for red light (660 nm) coincides with first maximum of some other wavelength λ′. The value of λ′ is

In a single slit diffraction experiment, position of minima is given by d sinθ=nλ so for first minima of red sinθ=1×λRd and as first maxima is midway between first and second minima, for wavelength λ′,  its position will be dsinθ′=λ′+2λ′2⇒sinθ′=3λ′2d According to given condition sinθ=sinθ′ ⇒λ′=23λR so λ′=23×6600=440nm=4400Å