#### Answer

a. The fringes on the screen become more tightly packed.
b. The fringes on the screen spread out, and become more loosely packed.

#### Work Step by Step

a. Equation 24-3b, $sin \theta = \frac{m \lambda}{D}$, predicts the location of the minima for nonzero integer values of m. Increasing the slit width D in a single-slit diffraction experiment will decrease the angle $\theta$ at which each minimum is seen, decreasing the spacing of the fringes.
b. Equation 24-3b, $sin \theta = \frac{m \lambda}{D}$, predicts the location of the minima for nonzero integer values of m. Increasing the wavelength $\lambda$ in a single-slit diffraction experiment will increase the angle $\theta$ at which each minimum is seen, increasing the spacing of the fringes.