Question

By increasing the slit separation, why do you have more peaks in the central diffraction envelope?

By decreasing the slit width, why do you have more peaks in the central diffraction envelope?

Answer 1

By increasing the slit separation, why do you have more peaks in the central diffraction envelope?

By increasing slit separation, you have less number of slits and with less number of slits, the fringe width decreases and thus more number of diffraction peaks will occur in the central diffraction envelope on the screen.

By decreasing the slit width, why do you have more peaks in the central diffraction envelope?

If we decrease the slit width size, it results in a broader central band. & this can accomodate more peaks in central diffraction envelope.