/sci/ - Science & Math

D.J. Griffith says
>"over small enough regions, any wave is essentially plane, as long as the wavelength is much less than the radius of the curvature of the wave front."
I can understand the part about the radius of curvature, so that the field vectors don't point in different directions in the region of interest, but I don't get why the wavelength needs to be small compared to the radius of curvature. It seems to me that, if anything, the plane wave approximation DOESN'T work if the wavelength is too small.

I've tried to sketch it, the blue line is the region of interest. The magnitude of the field peaks on the spherical wavefront touching the middle of the blue line. If the wavelength is small enough, there's a significant phase difference at the edges so the field magnitude is different too.

please respond