How to determine the spacing slit of dark fringe?

To determine the spacing of slits that produce dark fringes in a double-slit interference pattern, you can use the formula for the position of dark fringes: ( y_m = \frac{(m + 0.5) \lambda L}{d} ), where ( y_m ) is the distance from the central maximum to the m-th dark fringe, ( \lambda ) is the wavelength of the light used, ( L ) is the distance from the slits to the screen, and ( d ) is the slit separation. By measuring the distance between the central maximum and several dark fringes and knowing the wavelength and distance to the screen, you can rearrange the formula to solve for the slit spacing ( d ).