Question

In the Fraunhofer diffraction at a single slit, if yellow light illuminating the slit is replaced by blue light, then diffraction bands.
A) Remain unchanged
B) Become wider
C) Disappear
D) Became narrower

Answer 1

Hint
Fraunhofer diffraction is the type of diffraction number. The Pattern is independent of distance and depends on angle. The Property of color decides the bending angle over here and changes in its wavelength. The material used here too plays the role of bending by refractive index.

Complete Step By Step Solution
Let’s begin with what is Fraunhofer diffraction. It is the type of diffraction in which the diffraction of light takes Place in the limit of a small Fresnel number, where it is independent of distance but depends upon the angle to the screen from the aperture. As we know that the colors have their own wavelength interval like-

Red	~ 635 - 700 nm
Orange	~ 590 - 635 nm
Yellow	~ 560 - 590 nm
Green	~ 520 - 560 nm
Cyan	~ 490 - 520 nm
Blue	~ 450 - 490 nm
Violet	~ 400 - 450 nm

As we changed the yellow light to blue light.
the wavelength decreases and hence the diffraction band becomes narrower.
Because width of the Central diffraction’s maximum is inversely Proportional to the width of the slit. i.e., $\sin {\text{T}} = \dfrac{\lambda }{a}$
$\lambda \propto a$
so, decrease in $\lambda$ will result in a narrower central band.
So, option (D), become narrower is the correct option.

Note
The working of Fraunhofer diffraction and the individual wavelength of different color of lights is used over here. The holography is based upon the diffraction and x-ray which uses the diffraction studies. So slit is helpful in this process.