Two coherent monochromatic point sources $S_1$ and $S_2$ of wavelength $\lambda=600 \mathrm{~nm}$ are placed symmetrically on either side of the center of the circle as shown. The sources are separated by a distance $\mathrm{d}=1.8 \mathrm{~mm}$. This arrangement produces interference fringes visible as alternate bright and dark spots on the circumference of the circle. The angular separation between two consecutive bright spots is $\Delta \theta$. Which of the following options is/are correct?