Interference - White Light & Spectra

Introduction

• When white light is incident on a diffraction grating, it undergoes interference, creating a distinctive pattern of light and dark regions.
• In this context, the focus is on the spectral components produced by the interference of white light.

Central Maximum in White Light

• When white light is directed onto a grating, the central maximum in the resulting interference pattern appears as white light.
• The central maximum corresponds to the zero-order maximum and is the brightest part of the pattern.

Production of Spectra at Other Order Maxima

• Spectra are produced at the other order maxima observed in the interference pattern.
• Each order maximum represents a specific spectral component of white light, which is dispersed due to the interference effect of the grating.

Grating Relationship and Wavelength

• There is a fundamental relationship involving the grating that links the order maximum (n), the wavelength of light (λ), and the angle of observation (θ).
• This relationship can be expressed as:
• nλ = d sin(θ)
• Where:
  • n is the order number for the maximum (1 for first-order, 2 for second-order, etc.).
  • λ is the wavelength of the light.
  • d is the spacing between adjacent lines on the grating.
  • θ is the angle at which the maximum is observed.

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Interference - White Light & Spectra

Dependence on Wavelength

• The key insight from this relationship is that the angle θ depends only on the wavelength (λ) of the light.
• In other words, the specific angle at which a spectral component is observed is determined by its wavelength.
• Larger wavelengths result in larger angles of observation.

Applications and Significance

• The phenomenon of white light interference and the production of spectra are fundamental to spectroscopy.
• Spectroscopy is a powerful tool in scientific research and various industries for identifying chemical compositions, analysing materials, and studying celestial objects.

Summary

• When white light is incident on a diffraction grating, it undergoes interference, producing a pattern of bright and dark regions.
• Spectra are observed at the order maxima in the interference pattern, with each order corresponding to a specific spectral component.
• The grating relationship nλ = d sin(θ) links the order number, wavelength, and angle of observation.
• The angle θ depends solely on the wavelength, meaning that larger wavelengths result in larger observation angles.
• This phenomenon is fundamental in spectroscopy and has wide-ranging applications in scientific research and industry.