Work Step by Step
The fringes will be spaced closer together when the shorter-wavelength blue light is used. The equation at the bottom of page 550 explains this. $$\lambda = d sin \theta$$ Suppose we use a shorter wavelength, $\lambda$. The left-hand side of the equation is smaller, so the right-hand side must be smaller too. The distance between the slits, d, is fixed. The shorter wavelength gives a more tightly-packed pattern, i.e., $\theta$ decreases, because sin $\theta$ decreases.