Interference Pattern

The effect of wavelength, slit spacing, slit width, and number of slits on the intensity pattern

When the wavelength λ increases but the distance between slits d stays the same, the angle θ for bright fringes increases and the interference pattern spreads out.
Increasing the slit spacing d reduces θ, so the interference patterns are closer together.
The effect of the slit width b is that the single slit diffraction pattern modulates the N-slit pattern. In other words, the single slit curve becomes the envelope of the N-slit curve, i.e. the N-slit curve is pushed under the single-slit curve.
As the number of slits N increases, the primary maxima are observed at the same angles, but get narrower and brighter. In addition to that, (N-2) secondary maxima appear.