Explanation:

In Double Slit Fraunhofer Diffraction, when a monochromatic light beam passes through two slits and creates an interference pattern on a screen, some orders of the interference pattern may be missing. This phenomenon is known as "Absent Spectra" or "Missing Spectra."

Reason for Missing Spectra:

The missing spectra occur due to the destructive interference between the waves from different slits. When the waves from two slits meet at certain points on the screen, they interfere either constructively or destructively, resulting in bright or dark fringes, respectively. However, in some cases, destructive interference cancels out the intensity of certain orders of the interference pattern, making them absent.

Conditions for Missing Spectra:

The absence of certain orders of the interference pattern depends on the following conditions:

1. Path Difference: The path difference between the waves from the two slits determines the interference pattern. If the path difference between the waves is equal to an integer multiple of the wavelength (λ), the waves will interfere constructively, resulting in a bright fringe. However, if the path difference is equal to a half-integer multiple of the wavelength, the waves will interfere destructively, resulting in a dark fringe. This leads to missing spectra.

2. Order of Interference: The order of the interference depends on the number of wavelengths that fit between the slits and the screen. For example, the central bright fringe is known as the zeroth order, while the first-order fringes are located on either side of the central fringe. The intensity of the higher-order fringes decreases as the order increases.

3. Width of Slits: The width of the slits also affects the interference pattern. If the slits are very narrow, the interference pattern will have more missing spectra.

Conclusion:

In Double Slit Fraunhofer Diffraction, missing spectra or absent spectra occur due to the destructive interference between the waves from different slits. The path difference, order of interference, and width of slits play crucial roles in determining the presence or absence of certain orders of the interference pattern. The phenomenon of missing spectra provides valuable insights into the wave nature of light and the principles of interference.