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.
