Figure 27.56 shows a double slit located a distance $x$ from a screen, with the distance from the center of the screen given by $y$ . When the distance $d$ between the slits is relatively large, there will be numerous bright spots, called fringes. Show that, for small angles (where $\sin \theta \approx \theta$ , with $\theta$ in radians), the distance between fringes is given by $\Delta y=x \lambda / d$