DVD and Blue Ray disc questions?

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Ann

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You shine a Blue laser beam (wavelength 450nm) vertically on the surface of a DVD and then on the surface of a Blue Ray disc and count the number of reflections off of each. Which will produce a larger number of reflections?


I Think the DVD right? since it is like white light, it will reflect back all the light. while Blue Ray will absorb all the light and reflect back blue only. Am i right?
 
No. The Blu-ray will produce more reflections.

Blu-ray disks have a much higher density of pits than DVD's, so the reflectivity of their surface fluctuates more over a given space. As such, more reflections are observed. The DVD has fewer pits, so has fewer reflections.

You're thinking of the intensity of each reflection, not the number of reflections. In addition, negating absorbtion and re-emission, the disks will each only reflect the light that is actually shone on them. A blu-ray disk, being blue, will reflect pretty much all the blue light on it. If the DVD has uniform reflectivity, it will still reflect all the blue light.
 
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