Answer:
Photons strike the CD [tex]n=1.624 x10^{18}[/tex]
Explanation:
First of all, it is necessary to calculate the energy produced by a semiconductor laser for 69 minutes:
[tex]69minutes*\frac{60s}{1 minute}=4140s[/tex]
[tex]E=0.1x10^{-3}w*4140s=0.414J[/tex]
Next, it is possible to calculate the number of photons striking the CD surface during this time:
[tex]E=\frac{n*h*c}{l}[/tex]
[tex]l=780x10^{-9}m[/tex] long in CD
[tex]c=3x10^8 m/s[/tex] light velocity
[tex]h=6.626x10^{-34} J*s[/tex]
Solve to n'
[tex]n=\frac{E*l}{c*h}=\frac{0.414 J*780x10^{-9}m}{3x10^8m/s*6.626x10^{-34}}[/tex]
[tex]n=1.624 x10^{18}[/tex]
