4.4 Exercise 1

If the line spacing of a diffraction grating d is not precisely known, we can use a light source with a well-determined wavelength to measure it. Suppose the first-order constructive fringe of the $\text{H}_{\beta}$ emission line of hydrogen $\left(\lambda = 656.3 \text{nm}\right)$ is measured at $11.36 °$ using a spectrometer with a diffraction grating. What is the line spacing of this grating?