Question

How many photons strike the cd surface during the playing of a cd 69 minutes in length?

Answer 1

Answer:

Photons strike the CD $n=1.624 x10^{18}$

Explanation:

First of all, it is necessary to calculate the energy produced by a semiconductor laser for 69 minutes:

$69minutes*\frac{60s}{1 minute}=4140s$

$E=0.1x10^{-3}w*4140s=0.414J$

Next, it is possible to calculate the number of photons striking the CD surface during this time:

$E=\frac{n*h*c}{l}$

$l=780x10^{-9}m$ long in CD

$c=3x10^8 m/s$ light velocity

$h=6.626x10^{-34} J*s$

Solve to n'

$n=\frac{E*l}{c*h}=\frac{0.414 J*780x10^{-9}m}{3x10^8m/s*6.626x10^{-34}}$

$n=1.624 x10^{18}$