# why is frezneldistance used

An Aperture of size a illuminated by a parallel beam sends diffracted beam (the central maxima) in angular width approximately λ/a. Travelling a distance z, it aquires the width zλ/a due to diffraction. The distance at which this width equals the size of the aperture is called the fresnel distance.
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An Aperture of size a illuminated by a parallel beam sends diffracted beam (the central maxima) in angular width approximately ?/a. Travelling a?distance?z, it aquires the width z?/a due to diffraction. The?distance?at which this width equals the size of the aperture is called the?fresnel distance.
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Frezneldistance is that distances from the slit at which the spreading of a light due to diffraction because equal to the size of the slit
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