Firstly, for us to solve this problem, we must remember that the distance between each maximum can be written as:
[tex]\Delta y_{max}=\frac{D\lambda}{d}[/tex]Where D is the distance from the slit to the screen, d is the distance between each slit and lambda is the wavelength. Thus, we can calculate this as:
[tex]\Delta y_{max}=\frac{2.17*611.17*10^{-9}}{0.23*10^{-3}}=5.766mm[/tex]Thus, the distance from the central max (y0) and third max (y3) is three times this distance:
[tex]\Delta_{y0y3}=3*\Delta y_{max}=3*5.766mm=17.2988mm[/tex]Then, our final answer is delta=1.73cm
