Why does a DVD store almost 30 times more inf | vedclass

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(A) The storage capacity of an optical disc is determined by the size of the pits and lands,which is limited by the diffraction limit of the laser bea

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$DVD$ uses a shorter-wavelength laser of $6350 \,\mathring{A}$,while a $CD$ uses an infrared laser of $7800 \,\mathring{A}$.

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(A) The storage capacity of an optical disc is determined by the size of the pits and lands,which is limited by the diffraction limit of the laser beam used to read/write the data.According to the diffraction limit,the minimum spot size $d$ is proportional to the wavelength $\lambda$ of the laser $(d \propto \lambda)$.$A$ $DVD$ uses a red laser with a wavelength of approximately $6350 \,\mathring{A}$,whereas a $CD$ uses an infrared laser with a wavelength of $7800 \,\mathring{A}$.Since the $DVD$ laser has a shorter wavelength,it can focus on a smaller spot size,allowing for a much higher density of pits and lands on the disc surface.Consequently,a $DVD$ can store significantly more information (approximately $30$ times more) than a $CD$ of the same physical size.Therefore,option $(A)$ is the correct explanation.

Why does a $DVD$ store almost $30$ times more information than a $CD$?

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