Single-slit Diffraction - SS1 Physics Lesson Note

Single-slit diffraction is a phenomenon that occurs when a beam of light passes through a narrow slit and spreads out, creating a characteristic diffraction pattern on a screen or surface placed beyond the slit. It is a fundamental example of wave behaviour and provides insights into the wave nature of light.

Here are the key aspects of single-slit diffraction:

1. Diffraction Pattern: When light passes through a single narrow slit, it produces a diffraction pattern consisting of a central maximum and a series of secondary maxima and minima on either side. The central maximum is the brightest region, and the intensity decreases in the secondary maxima and minima.

2. Width of the Slit: The width of the slit plays a crucial role in determining the characteristics of the diffraction pattern. If the slit is very narrow compared to the wavelength of light, the diffraction pattern will be more pronounced.

3. Spreading of Light: As the light passes through the slit, it spreads out in a series of circular wavefronts. Each point on the slit can be thought of as a source of secondary spherical wavelets that propagate in all directions.

4. Interference: The secondary wavelets from different points on the slit interfere with each other, resulting in constructive interference at certain angles and destructive interference at others. This interference pattern produces the bright and dark fringes of the diffraction pattern.

5. Angular Spacing: The angular spacing between the secondary maxima and minima depends on the wavelength of light and the width of the slit. The smaller the slit width or the longer the wavelength, the wider the angular spacing between the fringes.

6. Intensity Distribution: The intensity of the diffracted light is not uniform across the diffraction pattern. The central maximum is the brightest region, while the intensity decreases in the secondary maxima and minima. The exact intensity distribution depends on the specific parameters of the experiment.

Single-slit diffraction is commonly observed in various real-world scenarios, such as:

-       Aperture Diffraction: When light passes through a small opening, such as a pinhole or a small hole in a barrier, it undergoes diffraction and creates a pattern of bright and dark regions on a screen.

-       Photography: Single-slit diffraction can affect the sharpness and resolution of photographs. It contributes to the phenomenon known as the "diffraction limit" in optical systems, where the size of the aperture limits the level of detail that can be captured.

-       Spectroscopy: Single-slit diffraction is used in spectrometers to disperse light into its component wavelengths and analyse the resulting spectrum. The diffraction pattern provides valuable information about the wavelengths present in the incident light.

-       Electron and Particle Diffraction: Single-slit diffraction is not limited to light waves but can also be observed with other types of waves, including electrons and other particles. This has been instrumental in the development of electron microscopy and the study of atomic and molecular structures.

Overall, single-slit diffraction demonstrates the wave nature of light and provides valuable insights into how waves interact with narrow openings. It is a fundamental concept in the field of optics and contributes to our understanding of diffraction phenomena.