## Conceptual Physics (12th Edition)

The fringes will be spaced farther apart when the longer-wavelength yellow light is used. The equation at the bottom of page 550 explains this. $$\lambda = d sin \theta$$ Suppose we use a longer wavelength, $\lambda$. The left-hand side of the equation is larger, so the right-hand side must be larger too. The distance between the slits, d, is fixed. The longer wavelength gives a more spread-out pattern, i.e., $\theta$ increases, because sin $\theta$ increases.