## Diffraction of Light through Diffraction Grating The diffraction grating operates on the principle of interference. When monochromatic light passes through its multiple slits, the light waves interfere constructively and destructively, producing a pattern of bright fringes (maxima) and dark fringes (minima). ### The Diffraction Grating Equation The spacing between two adjacent slits is called the **grating element** ($d$). If a grating has $N$ lines per unit length (e.g., lines per mm), the grating element is calculated as: $$d = \frac{1}{N}$$ The angles at which bright fringes (maxima) occur are described by the diffraction grating equation: $$ d \sin \theta = n \lambda $$ | Variable | Description | | :--- | :--- | | **d** | The spacing between adjacent slits in the grating (Grating Element) | | **$\theta$** | The angle of diffraction for a bright fringe relative to the central maximum | | **n** | The order of the bright fringe (an integer: 0, 1, 2, ...) | | **$\lambda$** | The wavelength of the incident light | By measuring the angle $\theta$ for a specific order $n$ and knowing the slit spacing $d$, the wavelength $\lambda$ can be calculated. This makes diffraction gratings essential instruments in **spectroscopy**. ### Comparison with Double Slit A diffraction grating produces maxima at the same angles as a double-slit setup when the slit spacing is identical. However, the maxima from a diffraction grating are significantly **narrower and sharper**. As the number of slits increases, the maxima become even narrower and the dark regions between them become darker. ### Maximum Order of Diffraction Since the maximum value of $\sin \theta$ is 1, the highest order $n$ that can be observed is limited by the grating element and wavelength: $$n_{max} \leq \frac{d}{\lambda}$$

18.2.1 Diffraction Of Light Through Diffraction Grating | Diffraction And Interference | Physics 12