Example 43: A diffraction grating having 15000 lines to an inch is used to photograph a spectrum. Calculate the angular dispersion in the second order spectrum of wavelength region 5.9×10−3cm. If the focal length of convex lens is 25 cm , calculate the linear dispersion in the spectrograph and also the separation between the spectral lines 5890A˚ and 5896A˚ in second order.