Diffraction of Light Waves - SS2 Physics Lesson Note

Diffraction is a fundamental phenomenon that occurs when waves encounter an obstacle or pass through an aperture, causing them to bend and spread out. In the context of light waves, diffraction refers to the bending and spreading of light as it encounters obstacles or passes through narrow openings.

Nature of Light:

Light is an electromagnetic wave that exhibits wave-like properties, such as interference, diffraction, and polarisation. According to the wave theory of light, light waves propagate as oscillating electric and magnetic fields.

Huygens' Principle:

Huygens' principle states that every point on a wavefront can be considered as a source of secondary spherical wavelets. When a wave encounters an obstacle or passes through an aperture, each point on the wavefront acts as a source of secondary wavelets that spread out in all directions.

Diffraction Patterns:

When light waves encounter an obstacle or pass through a narrow opening, they diffract and produce a characteristic diffraction pattern. The resulting pattern consists of alternating bright and dark regions, known as diffraction fringes or bands.

Single-Slit Diffraction:

When light passes through a single narrow slit, it spreads out and produces a diffraction pattern. The central maximum is bright, while on either side of it, alternating bright and dark fringes are observed. The width of the central maximum is greater than the width of the subsequent fringes.

Double-Slit Diffraction:

When light passes through two closely spaced parallel slits, it undergoes double-slit diffraction. The resulting pattern exhibits interference and diffraction effects, leading to a series of bright and dark fringes. The central maximum is bright, and the adjacent fringes exhibit decreasing intensity.

Diffraction Gratings:

Diffraction gratings are optical devices consisting of a large number of equally spaced parallel slits or grooves. When light passes through a diffraction grating, it produces a highly structured diffraction pattern with multiple bright and dark fringes.

Applications:

Diffraction is utilised in various scientific and technological applications:

a.    Diffraction is used in spectroscopy to separate and analyse different wavelengths of light, enabling the study of atomic and molecular structures.

b.    X-ray diffraction is used to study the atomic arrangements in crystals and determine their crystal structures.

c.    Diffraction techniques are employed in the field of optics to create diffraction gratings, which find applications in wavelength measurement, beam splitting, and imaging.

Diffraction of light waves is a fundamental phenomenon that plays a crucial role in understanding the behaviour of waves and has numerous practical applications. By studying diffraction, scientists and engineers can gain valuable insights into the nature of light and develop technologies that rely on the manipulation and control of wave behaviour.