# Bending of waves around obstacles and the effect of wavelength

1. Feb 23, 2012

### ARAVIND113122

why does the wavelength of light or sound waves affect the degree of bending?I know the mathematical formula for fringe width,but i want to know the physical reasons behind the phenomenon of bending.
Taking the example of light passing through a small slit,the huygens principle talks about wavelets,but why do wavelets of red light spread more than those of blue light?[i know this is in some way related to the wavelength of waves,but i don't exactly understand the concept physically]
to be more specific,since wavelength is the distance between successive wave fronts,how does this distance affect the spread of waves after passing through the slit?

2. Feb 24, 2012

### Claude Bile

It is to do with scaling. The basic principle of diffraction is that a 1 micron wavelength wave diffracted by a 1 micron object should diffract the same if it were a 1 metre wavelength incident on a 1 metre object.

This is why there is always an ever-present a/$\lambda$ factor in diffraction equations.

In truth, the Huygens-Fresnel theory can't explain the wavelength dependence that well, the Kirchoff integral though is more accurate since it is a direct solution to the Helmholtz equation.

Claude.