In Fresnel diffraction,if the distance betwee | vedclass

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(B) In the case of diffraction by a circular disc (Poisson's spot),the intensity at the center depends on the number of Half-Period Zones $(HPZ)$ bloc

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Decrease

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(B) In the case of diffraction by a circular disc (Poisson's spot),the intensity at the center depends on the number of Half-Period Zones $(HPZ)$ blocked by the disc.The number of $HPZ$ blocked is given by $n = \frac{A}{\pi \lambda d}$,where $A$ is the area of the disc,$\lambda$ is the wavelength,and $d$ is the distance between the disc and the screen.Since $A, \pi,$ and $\lambda$ are constants,we have $n \propto \frac{1}{d}$.When the distance $d$ is decreased,the number of blocked $HPZ$ $(n)$ increases.As more $HPZ$ are blocked,the destructive interference at the center increases,which leads to a decrease in the intensity of the central bright spot.

In Fresnel diffraction,if the distance between the disc and the screen is decreased,the intensity of the central bright spot will

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